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Research Article

Research on drinking water purification technologies for household use by reducing total dissolved solids (TDS)

Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing

* E-mail: [email protected]

Affiliation Redlands East Valley High School, Redlands, California, United States of America

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  • Bill B. Wang

PLOS

  • Published: September 28, 2021
  • https://doi.org/10.1371/journal.pone.0257865
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Fig 1

This study, based in San Bernardino County, Southern California, collected and examined tap water samples within the area to explore the feasibility of adopting non-industrial equipment and methods to reduce water hardness and total dissolved solids(TDS). We investigated how water quality could be improved by utilizing water boiling, activated carbon and sodium bicarbonate additives, as well as electrolysis methods. The results show that heating is effective at lower temperatures rather than long boils, as none of the boiling tests were lower than the original value. Activated carbon is unable to lower TDS, because it is unable to bind to any impurities present in the water. This resulted in an overall TDS increase of 3.5%. However, adding small amounts of sodium bicarbonate(NaHCO 3 ) will further eliminate water hardness by reacting with magnesium ions and improve taste, while increasing the pH. When added to room temperature tap water, there is a continuous increase in TDS of 24.8% at the 30 mg/L mark. The new findings presented in this study showed that electrolysis was the most successful method in eliminating TDS, showing an inverse proportion where an increasing electrical current and duration of electrical lowers more amounts of solids. This method created a maximum decrease in TDS by a maximum of 22.7%, with 3 tests resulting in 15.3–16.6% decreases. Furthermore, when water is heated to a temperature around 50°C (122°F), a decrease in TDS of around 16% was also shown. The reduction of these solids will help lower water hardness and improve the taste of tap water. These results will help direct residents to drink more tap water rather than bottled water with similar taste and health benefits for a cheaper price as well as a reduction on plastic usage.

Citation: Wang BB (2021) Research on drinking water purification technologies for household use by reducing total dissolved solids (TDS). PLoS ONE 16(9): e0257865. https://doi.org/10.1371/journal.pone.0257865

Editor: Mahendra Singh Dhaka, Mohanlal Sukhadia University, INDIA

Received: June 22, 2021; Accepted: September 14, 2021; Published: September 28, 2021

Copyright: © 2021 Bill B. Wang. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All relevant data are within the manuscript and its Supporting Information files.

Funding: The author received no specific funding for this work.

Competing interests: The authors have declared that no competing interests exist.

Introduction

The concentration of total dissolved solids(TDS) present in water is one of the most significant factors in giving water taste and also provides important ions such as calcium, magnesium, potassium, and sodium [ 1 – 3 ]. However, water with high TDS measurements usually indicates contamination by human activities, such as soil and agricultural runoff caused by irrigation, unregulated animal grazing and wildlife impacts, environmentally damaging farming methods such as slash and burn agriculture, and the overuse of nitrate-based fertilizer [ 4 , 5 ], etc. Around tourist areas as well as state parks, these factors will slowly add up over time and influence the water sources nearby [ 5 ]. Water that flows through natural springs and waterways with high concentrations of organic salts within minerals and rocks, or groundwater that originates from wells with high salt concentration will also result in higher particle measurements [ 6 ].

Water sources can be contaminated by substances and ions such as nitrate, lead, arsenic, and copper [ 7 , 8 ] and may cause many health problems related to heavy metal consumption and poisoning. Water reservoirs and treatments plants that do not consider water contamination by motor vehicles, as well as locations that struggle to provide the necessary components required for water treatment will be more prone to indirect contamination [ 9 – 11 ]. Many plants are effective in ensuring the quality and reduction of these contaminants, but often leave out the secondary considerations, The United States Environmental Protection Agency(US EPA)’s secondary regulations recommend that TDS should be below 500 mg/L [ 2 ], which is also supported by the World Health Organization(WHO) recommendation of below 600 mg/L and an absolute maximum of less than 1,000 mg/L [ 3 ]. These substances also form calcium or magnesium scales within water boilers, heaters, and pipes, causing excess buildup and drain problems, and nitrate ions may pose a risk to human health by risking the formation of N -nitroso compounds(NOC) and less public knowledge about such substances [ 12 – 15 ]. Nitrates can pose a non-carcinogenic threat to different communities, but continue to slip past water treatment standards [ 15 ]. Furthermore, most people do not tolerate or prefer water with high hardness or chlorine additives [ 16 ], as the taste changes tremendously and becomes unpreferable. Even so, TDS levels are not accounted for in mandatory water regulations, because the essential removal of harmful toxins and heavy metals is what matters the most in water safety. Some companies indicate risks in certain ions and alkali metals, showing how water hardness is mostly disregarded and is not as well treated as commercial water bottling companies [ 17 , 18 ].

In Southern California, water quality is not as well maintained than the northern counties as most treatment plants in violation of a regulation or standard are located in Central-Southern California [ 19 ], with southern counties having the largest number of people affected [ 20 ]. This study is focused on the Redlands area, which has had no state code violations within the last decade [ 21 ]. A previous study has analyzed TDS concentrations throughout the Santa Ana Basin, and found concentrations ranging from 190–600 ppm as treated wastewater and samples obtained from mountain sites, taking into account the urban runoff and untreated groundwater as reasons for elevated levels of TDS but providing no solution in helping reduce TDS [ 22 ]. Also, samples have not been taken directly through home water supplies, where the consumer is most affected. Other water quality studies in this region have been focused on the elimination of perchlorates in soil and groundwater and distribution of nitrates, but such research on chemicals have ceased for the last decade, demonstrated by safe levels of perchlorates and nitrates in water reports [ 23 , 24 ]. In addition to these studies, despite the improving quality of the local water treatment process, people prefer bottled water instead of tap water because of the taste and hardness of tap water [ 25 ]. Although water quality tests are taken and documented regularly, the taste of the water is not a factor to be accounted for in city water supplies, and neither is the residue left behind after boiling water. The residue can build up over time and cause appliance damage or clogs in drainage pipes.

This study will build upon previous analyses of TDS studies and attempt to raise new solutions to help develop a more efficient method in reducing local TDS levels, as well as compare current measurements to previous analyses to determine the magnitude to which local treatment plants have improved and regulated its treatment processes.

Several methods that lower TDS are reviewed: boiling and heating tap water with and without NaHCO₃, absorption by food-grade activated carbon [ 26 , 27 ], and battery-powered electrolysis [ 28 – 30 ]. By obtaining water samples and determining the difference in TDS before and after the listed experiments, we can determine the effectiveness of lowering TDS. The results of this study will provide options for residents and water treatment plants to find ways to maintain the general taste of the tap water, but also preserve the lifespan of accessories and pipelines. By determining a better way to lower TDS and treat water hardness, water standards can be updated to include TDS levels as a mandatory measurement.

Materials and methods

All experiments utilized tap water sourced from Redlands homes. This water is partially supplied from the Mill Creek (Henry Tate) and Santa Ana (Hinckley) Water Sheds/Treatment Plants, as well as local groundwater pumps. Water sampling and sourcing were done at relatively stable temperatures of 26.9°C (80.42°F) through tap water supplies. The average TDS was measured at 159 ppm, which is slightly lower than the reported 175 ppm by the City of Redlands. Permission is obtained by the author from the San Bernardino Municipal Water Department website to permit the testing procedures and the usage of private water treatment devices for the purpose of lowering water hardness and improving taste and odor. The turbidity was reported as 0.03 Nephelometric Turbidity Units (NTU) post-treatment. Residual nitrate measured at 2.3mg/L in groundwater before treatment and 0.2 mg/L after treatment and perchlorate measured at 0.9 μg/L before treatment, barely staying below the standard of 1 μg/L; it was not detected within post-treatment water. Lead content was not detected at all, while copper was detected at 0.15 mg/L.

For each test, all procedures were done indoors under controlled temperatures, and 20 L of fresh water was retrieved before each test. Water samples were taken before each experimental set and measured for TDS and temperature, and all equipment were cleaned thoroughly with purified water before and after each measurement. TDS consists of inorganic salts and organic material present in solution, and consists mostly of calcium, magnesium, sodium, potassium, carbonate, chloride, nitrate, and sulfate ions. These ions can be drawn out by leaving the water to settle, or binding to added ions and purified by directly separating the water and ions. Equipment include a 50 L container, 1 L beakers for water, a graduated cylinder, a stir rod, a measuring spoon, tweezers, a scale, purified water, and a TDS meter. A standard TDS meter is used, operated by measuring the conductivity of the total amount of ionized solids in the water, and is also cleaned in the same manner as aforementioned equipment. The instrument is also calibrated by 3 pH solutions prior to testing.All results were recorded for and then compiled for graphing and analysis.

Heating/Boiling water for various lengths of time

The heating method was selected because heat is able to break down calcium bicarbonate into calcium carbonate ions that are able to settle to the bottom of the sample. Four flasks of 1 L of tap water were each heated to 40°C, 50°C, 60°C, and 80°C (104–176°F) and observed using a laser thermometer. The heated water was then left to cool and measurements were made using a TDS meter at the 5, 10, 20, 30, and 60-minute marks.

For the boiling experiments, five flasks of 1 L of tap water were heated to boil at 100°C (212°F). Each flask, which was labeled corresponding to its boiling duration, was marked with 2, 4, 6, 10, and 20 minutes. Each flask was boiled for its designated time, left to cool under open air, and measurements were made using a TDS meter at the 5, 10, 20, 30, 60, and 120-minute marks. The reason that the boiling experiment was extended to 120 minutes was to allow the water to cool down to room temperature.

Activated carbon as a water purification additive

This test was performed to see if food-grade, powdered activated carbon had any possibility of binding with and settling out residual particles. Activated carbon was measured using a milligram scale and separated into batches of 1, 2, 4, 5, 10, 30, and 50 mg. Each batch of the activated carbon were added to a separate flask of water and stirred for five minutes, and finally left to settle for another five minutes. TDS measurements were recorded after the water settled.

Baking soda as a water purification additive

To lower scale error and increase experimental accuracy, a concentration of 200 mg/L NaHCO₃ solution was made with purified water and pure NaHCO₃. For each part, an initial TDS measurement was taken before each experiment.

In separate flasks of 1 L tap water, each labeled 1, 2, 4, 5, 10, and 30 mg of NaHCO 3 , a batch was added to each flask appropriately and stirred for 5 minutes to ensure that everything dissolved. Measurements were taken after the water was left to settle for another 5 minutes for any TDS to settle.

Next, 6 flasks of 1 L tap water were labeled, with 5 mg (25 mL solution) of NaHCO₃ added to three flasks and 10 mg (50 mL solution) of NaHCO₃ added to the remaining three. One flask from each concentration of NaHCO₃ was boiled for 2 mins., 4 mins., or 6 mins., and then left to cool. A TDS measurement was taken at the 5, 10, 20, 30, 60, and 120-minute marks after removal from heat.

Electrolysis under low voltages

This test was performed because the ionization of the TDS could be manipulated with electricity to isolate an area of water with lower TDS. For this test, two 10cm long graphite pieces were connected via copper wiring to a group of batteries, with each end of the graphite pieces submerged in a beaker of tap water, ~3 cm apart.

Using groups of 1.5 V double-A batteries, 4 beakers with 40mL of tap water were each treated with either 7.5, 9.0, 10.5, and 12.0 V of current. Electrolysis was observed to be present by the bubbling of the water each test, and measurements were taken at the 3, 5, 7, and 10 minute marks.

Results/Discussion

Heating water to various temperatures until the boiling point.

The goal for this test was to use heat to reduce the amount of dissolved oxygen and carbon dioxide within the water, as shown by this chemical equation: Heat: Ca(HCO 3 ) 2 → CaCO 3 ↓ + H 2 O + CO 2 ↑.

This would decompose ions of calcium bicarbonate down into calcium carbonate and water and carbon dioxide byproducts.

Patterns and trends in decreasing temperatures.

The following trend lines are based on a dataset of changes in temperature obtained from the test results and graphed as Fig 1 .

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https://doi.org/10.1371/journal.pone.0257865.g001

To predict the precise temperature measurements of the tap water at 26.9°C, calculations were made based on Fig 1 . The fitting equations are in the format, y = a.e bx . The values for the fitting coefficients a and b, and correlation coefficient R 2 are listed in Table 1 as column a, b and R 2 . The calculated values and the target temperature are listed in Table 1 .

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https://doi.org/10.1371/journal.pone.0257865.t001

Fig 2 was obtained by compiling TDS results with different temperatures and times.

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The fitting equations for Fig 2 are also in the format, y = a.e bx . The fitting coefficients a and b, and correlation coefficient R 2 values are listed in Table 2 . Based on the fitting curves in Fig 2 and the duration to the target temperature in Table 1 , We calculated the TDS at 26.9°C as listed in column calculated TDS in Table 2 based on the values we reported on Fig 2 .

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https://doi.org/10.1371/journal.pone.0257865.t002

Based on the heating temperature and the calculated TDS with the same target water temperature, we obtained the following heating temperature vs TDS removal trend line and its corresponding fitting curve in Table 2 .

In Fig 1 , a trend in the rate of cooling is seen, where a higher heating temperature creates a steeper curve. During the first five minutes of cooling, the water cools quicker as the absorbed heat is quickly released into the surrounding environment. By the 10-minute mark, the water begins to cool in a linear rate of change. One detail to note is that the 100°C water cools quicker than the 80°C and eventually cools even faster than the 60°C graph. Table 1 supports this observation as the duration to target temperature begins to decrease from a maximum point of 94.8 mins to 80.95 mins after the 80°C mark.

As shown in Fig 2 , all TDS values decrease as the temperature starts to cool to room temperature, demonstrating a proportional relationship where a lower temperature shows lower TDS. This can partially be explained by the ions settling in the flasks. Visible particles can also be observed during experimentation as small white masses on the bottom, as well as a thin ring that forms where the edge of the water contacts the flask. When the water is heated to 40°C and cooled, a 3.8% decrease in TDS is observed. When 50°C is reached, the TDS drops at its fastest rate from an initial value of 202 ppm to 160 ppm after 60 minutes of settling and cooling. The TDS measurements in these experiements reach a maximum of 204 ppm at the 60°C mark. However, an interesting phenomenon to point out is that the water does not hit a new maximum at 100°C. meaning that TDS reaches a plateau at 60°C. Also, the rate of decrease begins to slow down after 20 minutes, showing that an unknown factor is affecting the rate of decrease. It is also hypothesized that the slight increase in TDS between the 5–20 minute range is caused by a disturbance in the settling of the water, where the temperature starts to decrease at a more gradual and constant rate. The unstable and easy formation of CaCO 3 scaling has also been the subject of a study of antiscaling methods, which also supports the result that temperature is a significant influence for scale formation [ 12 ].

In Table 2 , calculations for TDS and the time it takes for each test to cool were made. Using the data, it is determined that the test with 50°C water decreased the most by 16% from the initial measurement of 159ppm. This means that it is most effective when water is heated between temperatures of 40–60°C when it comes to lowering TDS, with a difference of ~7–16%. When water is heated to temperatures greater than 80°C, the water begins to evaporate, increasing the concentration of the ions, causing the TDS to increase substantially when cooled to room temperature.

Finally, in Fig 3 , a line of best fit of function f(x) = -0.0007x 3 + 0.1641x 2 –10.962x + 369.36 is used with R 2 = 0.9341. Using this function, the local minimum of the graph would be reached at 48.4°C.

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https://doi.org/10.1371/journal.pone.0257865.g003

This data shows that heating water at low temperatures (i.e. 40–50°C) may be more beneficial than heating water to higher temperatures. This study segment has not been presented in any section within the United States EPA Report on water management for different residual particles/substances. However, warmer water temperatures are more prone to microorganism growth and algal blooms, requiring more intensive treatment in other areas such as chlorine, ozone, and ultraviolet disinfection.

Using the specific heat capacity equation, we can also determine the amount of energy and voltage needed to heat 1 L of water up to 50°C: Q = mcΔT, where c, the specific heat capacity of water, is 4.186 J/g°C, ΔT, the change in temperature from the experimental maximum to room temperature, is 30°C, and m, the mass of the water, is 1000 g. This means that the amount of energy required will be 125580 J, which is 0.035 kWh or 2.1 kW.

After taking all of the different measurements obtained during TDS testing, and compiling the data onto this plot, Fig 4 is created with a corresponding line of best fit:

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In Fig 4 , it can be observed that the relationship between the temperature of the water and its relative TDS value is a downwards facing parabolic graph. As the temperature increases, the TDS begins to decrease after the steep incline at 50–60°C. The line of best fit is represented by the function f(x) = -0.0142x 2 + 2.258x + 105.84. R 2 = 0.6781. Because the R 2 value is less than expected, factors such as the time spent settling and the reaction rate of the ions should be considered. To determine the specifics within this experiment, deeper research and prolonged studies with more highly accurate analyses must be utilized to solve this problem.

Boiling water for various amounts of time

Trend of boiling duration and rate of cooling..

Using the same methods to create the figures and tables for the previous section, Fig 5 depicts how the duration of time spent boiling water affects how fast the water cools.

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https://doi.org/10.1371/journal.pone.0257865.g005

As seen in Fig 5 , within the first 10 minutes of the cooling time, the five different graphs are entwined with each other, with all lines following a similar pattern. However, the graph showing 20 minutes of boiling is much steeper than the other graphs, showing a faster rate of cooling. This data continues to support a previous claim in Fig 2 , as this is most likely represented by a relationship a longer the boil creates a faster cooling curve. This also shows that the first 5 minutes of cooling have the largest deviance compared to any other time frame.

The cooling pattern is hypothesized by possible changes in the orderly structure of the hydrogen bonds in the water molecules, or the decreased heat capacity of water due to the increasing concentration of TDS.

Effect on TDS as boiling duration increases.

In Fig 6 , all lines except for the 20-minute line are clustered in the bottom area of the graph. By excluding the last measurement temporarily due to it being an outlier, we have observed that the difference between the initial and final TDS value of each test decreases.

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https://doi.org/10.1371/journal.pone.0257865.g006

Despite following a similar trend of an increase in TDS at the start of the tests and a slow decrease overtime, this experiment had an interesting result, with the final test measuring nearly twice the amount of particles compared to any previous tests at 310 ppm, as shown in Fig 6 . It is confirmed that the long boiling time caused a significant amount of water to evaporate, causing the minerals to be more concentrated, thus resulting in a 300 ppm reading. Fig 6 follows the same trend as Fig 2 , except the TDS reading veers away when the boiling duration reaches 20 minutes. Also, with the long duration of heating, the water has developed an unfavorable taste from intense concentrations of CaCO₃. This also causes a buildup of a thin crust of CaCO₃ and other impurities around the container that is difficult to remove entirely. This finding is in accordance with the introductory statement of hot boiling water causing mineral buildups within pipes and appliances [ 9 ]. A TDS reading of 300ppm is still well below federal secondary standards of TDS, and can still even be compared to bottled water, in which companies may fluctuate and contain 335ppm within their water [ 1 , 2 ].

This experiment continues to stupport that the cooling rate of the water increases as the time spent boiling increases. Based on this test, a prediction can be made in which an increased concentration of dissolved solids lowers the total specific heat capacity of the sample, as the total volume of water decreases. This means that a method can be derived to measure TDS using the heat capacity of a tap water mixture and volume, in addition to current methods of using the electrical conductivity of aqueous ions.

Adding food-grade activated carbon to untreated tap water

Fig 7 presents a line graph with little to no change in TDS, with an initial spike from 157 to 163 ppm. The insoluble carbon remains in the water and shows no benefit.

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https://doi.org/10.1371/journal.pone.0257865.g007

The food-grade activated carbon proved no benefit to removing TDS from tap water, and instead added around 5–7 ppm extra, which settled down to around +4 ppm at 120 minutes. The carbon, which is not 100% pure from inorganic compounds and materials present in the carbon, can dissolve into the water, adding to the existing concentration of TDS. Furthermore, household tap water has already been treated in processing facilities using a variety of filters, including carbon, so household charcoal filters are not effective in further reducing dissolved solids [ 18 ].

Adding sodium bicarbonate solution to boiled tap water

As seen in Fig 8 , after adding 1 mg of NaHCO 3 in, the TDS rises to 161 ppm, showing a minuscule increase. When 4 mg was added, the TDS drops down to 158 ppm. Then, when 5 mg was added, a sudden spike to 172 ppm was observed. This means that NaHCO 3 is able to ionize some Ca 2+ and Mg 2+ ions, but also adds Na + back into the water. This also means that adding NaHCO 3 has little to no effect on TDS, with 4mg being the upper limit of effectiveness.

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To examine whether or not the temperature plays a role in the effectiveness in adding NaHCO 3 , a boiling experiment was performed, and the data is graphed in Fig 9 .

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Fig 9 presents the relationship between the amount of common baking soda(NaHCO₃) added, the boiling time involved, and the resulting TDS measurements. After boiling each flask for designated amounts of time, the results showed a downward trend line from a spike but does not reach a TDS value significantly lower than the initial sample. It is apparent that the NaHCO₃ has not lowered the TDS of the boiling water, but instead adds smaller quantities of ions, raising the final value. This additive does not contribute to the lowering of the hardness of the tap water. However, tests boiled with 5 mg/L of baking soda maintained a downward pattern as the water was boiled for an increasing amount of time, compared to the seemingly random graphs of boiling with 10 mg/L.

In some households, however, people often add NaHCO₃ to increase the pH for taste and health benefits. However, as shown in the test results, it is not an effective way of reducing TDS levels in the water [ 10 , 16 ], but instead raises the pH, determined by the concentration added. Even under boiling conditions, the water continues to follow the trend of high growth in TDS, of +25–43 ppm right after boiling and the slow drop in TDS (but maintaining a high concentration) as the particles settle to the bottom.

Utilizing the experimental results, we can summarize that after adding small batches of NaHCO3 and waiting up to 5 minutes will reduce water hardness making it less prone to crystallizing within household appliances such as water brewers. Also, this process raises the pH, which is used more within commercial water companies. However, the cost comes at increasing TDS.

Using electrolysis to treat TDS in tap water

Different voltages were passed through the water to observe the change in TDS overtime, with the data being compiled as Fig 10 .

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The process of electrolysis in this experiment was not to and directly remove the existing TDS, but to separate the water sample into three different areas: the anode, cathode, and an area of clean water between the two nodes [ 19 ]. The anions in the water such as OH - , SO 4 2- , HCO 3 - move to the anode, while the cations such as H + , Ca 2+ 、Mg 2+ 、Na + move to the cathode. The middle area would then be left as an area that is more deprived of such ions, with Fig 10 proving this.

As shown in Fig 10 , electrolysis is effective in lower the TDS within tap water. Despite the lines being extremely tangled and unpredictable, the general trend was a larger decrease with a longer duration of time. At 10 minutes, all lines except 10.5 V are approaching the same value, meaning that the deviation was most likely caused by disturbances to the water during measurement from the low volume of water. With each different voltage test, a decrease of 12.7% for 6.0 V, 14.9% for 9.0 V, 22.7% for 10.5 V. and 19.5% for 12.0 V respectfully were observed. In the treatment of wastewate leachate, a study has shown that with 90 minutes of electrical treatment, 34.58% of TDS content were removed, supporting the effectiveness of electricity and its usage in wastewater treatment [ 29 ].

This experiment concludes that electrolysis is effective in lowering TDS, with the possibility to improve this process by further experimentation, development of a water cleaning system utilizing this cathode-anode setup to process water. This system would be a more specific and limited version of a reverse osmosis system by taking away ions through attraction, rather than a filter.

The Southern Californian tap water supply maintains TDS values below the federal regulations. However, crystalline scale buildup in household appliances is a major issue as it is hard to clean and eliminate. To easily improve the taste and quality of tap water at home as well as eliminating the formation of scales, the following methods were demonstrated as viable:

  • By heating water to around 50°C (122°F), TDS and water hardness will decrease the most. Also, the boiling process is effective in killing microorganisms and removing contaminants. This process cannot surpass 10 minutes, as the concentration of the ions in the water is too high, which poses human health risks if consumed. These, along with activated carbon and NaHCO₃ additives, are inefficient methods that have minimal effects for lowering TDS.
  • Electrolysis is one of the most effective methods of eliminating TDS. Experiments have proven that increased current and duration of time helps lower TDS. However, this method has yet to be implemented into conventional commercial water filtration systems.

Also, some observations made in these experiments could not be explained, and require further research and experimentation to resolve these problems. The first observation is that TDS and increasing water temperature maintain a parabolic relationship, with a maximum being reached at 80°C, followed by a gradual decrease. The second observation is that when water is boiled for an increased duration of time, the rate of cooling also increases.

This experiment utilized non-professional scientific equipment which are prone to mistakes and less precise. These results may deviate from professionally derived data, and will require further study using more advanced equipment to support these findings.

Acknowledgments

The author thanks Tsinghua University Professor and PLOS ONE editor Dr. Huan Li for assisting in experimental setups as well as data processing and treatment. The author also thanks Redlands East Valley High School’s Dr. Melissa Cartagena for her experimental guidance, and Tsinghua University Professor Dr. Cheng Yang for proofreading the manuscript.

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Literature review, data and empirical specification, concluding remarks, data availability statement, conflict of interest, tap water quality: in the eye of the beholder.

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Arnt O. Hopland , Sturla F. Kvamsdal; Tap water quality: in the eye of the beholder. J Water Health 1 September 2022; 20 (9): 1436–1444. doi: https://doi.org/10.2166/wh.2022.151

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The quality of tap water is important. We consider whether objective measures of water quality factor into satisfaction with tap water among a large sample of Norwegian citizens. Our data include over 40,000 observations from the last decade and constitute an unprecedented empirical basis for investigating the link between water quality and user satisfaction. Objective measures of water quality include tests on Escherichia coli , intestinal enterococci, pH, and color. Only color has a significant impact on citizens’ satisfaction with tap water. However, individual characteristics can to some degree predict tap water satisfaction. For example, the general level of satisfaction with public services and society, age, education, income, and gender are relevant characteristics. Our data are rich enough to allow for the use of fixed effects to control for unique municipal factors, such as geography and access to water sources, as well as time trends. Thus, we provide rather solid evidence that satisfaction with tap water is unrelated to several objective measures of quality, but that satisfaction is related to several individual characteristics.

Compare objective measures of tap water quality with user satisfaction.

Extensive, nationwide panel data.

Only a weak link between objective quality and user satisfaction.

Individual user characteristics are strong predictors of user satisfaction.

Tap water quality is important for health and well-being. Monitoring tap water quality is thus an essential public service. There is also an emphasis on the perception and level of satisfaction with tap water, which, for example, impacts the consumption of bottled water ( Delpla et al. 2020 ). Several studies have investigated the relationship between perceptions and objective measures of tap water quality (e.g., Montenegro et al. 2009 ; Proulx et al. 2010 ), but the empirical evidence is patchy and thin.

This paper studies citizen satisfaction with tap water using a biannual nationwide citizen survey in Norway. By linking the individual responses to municipal-level test data supplied by Statistics Norway (SSB), we can investigate the link between objective water quality and user satisfaction.

The test data capture the share of inhabitants that are connected to water supply systems with acceptable levels of Escherichia coli , intestinal enterococci, pH, and color in a given year. Interestingly, only the test result for color is significantly associated with the citizens’ satisfaction with the tap water. Instead, a set of individual characteristics do a much better job in predicting how satisfied respondents are with their tap water.

Most important is a measure of the respondents’ ‘general satisfaction/mood’, a variable that captures the respondents’ average satisfaction with 10 other categories. This reflects that respondents tend to report high or low satisfaction consistently, across unrelated categories. We also consistently find that men report higher satisfaction with the tap water than women.

When looking at age-groups, we find a mixed bag of results. The oldest group (76 years and older) is significantly more satisfied with the tap water than any group of younger respondents. Satisfaction does not grow steadily with age, though. Rather, respondents in the youngest group (18–35 years) are equally satisfied as respondents in the second-oldest (56–65 years) group, while those in the groups between (36–45 and 46–55 years) are consistently less satisfied with the tap water.

Respondents with higher education are consistently less satisfied with tap water than those with lower or no education. Interestingly, we find an opposite effect for income. Respondents from households with a joint income of above 1 million NOK (about 100,000 USD), i.e., the 14% highest incomes in the sample, tend to be more satisfied with the tap water. Married (including those living with their partner) do not deviate systematically from un-married. Finally, we observe a weak tendency that respondents who voted for a left-leaning political party at the last national election before the survey are more satisfied with the tap water than others.

Several earlier studies have looked at factors explaining user perceptions of tap water quality, but unlike our study, these are based on modest datasets, mostly with little or no variation over time. Since we combine a national survey conducted every second year with annual testing data, we have data for well over 40,000 individuals in over 400 Norwegian municipalities spread over five surveys conducted over a period spanning a full decade.

The richness of our data does not only ensure better grounds for generalizability than earlier studies, but it also allows us to use refined empirical techniques. Since we have survey data for 5 years and multiple responders per municipality in each round of the survey, we can use fixed effects techniques to control for all aspects that are unique and time-invariant for a municipality (municipal fixed effects). Hence, our inference is based on different individuals drinking tap water within the same municipality. We can also control effectively for general trends using time fixed effects, securing that our results are not driven by, e.g., a general national improvement in water quality over time. In addition, we can combine these sets of fixed effects into municipality-specific time trends. When using this specification, the inference is based on individuals within the same municipality in the same year, i.e., all variables that vary over time and across local governments but are similar for all individuals within a local government in a particular year are controlled for. We do not include test results in this specification, as this is captured by the municipality-specific time trend, and focus only on the individual characteristics of the respondent.

Our results are consistent with findings in several other studies. Many studies find that flavor and other sensory qualities (odor, color) are important explanatory variables of tap water quality ( Turgeon et al. 2004 ; Doria et al. 2009 ; Montenegro et al. 2009 ; Proulx et al. 2010 ; Piriou et al. 2015 ). These findings are consistent with our finding that color matters, as sensory qualities are directly observable to the consumers. Similar as us, the literature also frequently finds that many other, and less obvious, factors affect the assessment of water quality.

Socio-economic characteristics of the respondents are often important determinants. Indeed, Ochoo et al. (2017) found no correlation between actual water quality and citizen satisfaction in a study of 100 households in 45 communities in Newfoundland, Canada. They found that more highly educated and well-paid inhabitants approved of the water quality to a larger extent than less educated, low-income citizens. Delpla et al. (2020) studying perceptions of tap water among 1,014 citizens in Québec, Canada, found a weak link between quality and satisfaction with tap water. Water consumption, however, was strongly linked to sensory qualities, but also impacted by household water treatment (filtering and cooling), knowledge about water quality, and risk perceptions.

Also, earlier studies have investigated variables such as age, education, household income, and gender as predictors of water quality perception ( Auslander & Langlois 1993 ; Turgeon et al. 2004 ; Dogaru et al. 2009 ; García-Rubio et al. 2016 ). All these studies are based on relatively small data sets. Romano & Masserini (2020) lists these and others, and the largest sample size in their list is around 1,000. Furthermore, some results are in conflict. For example, Dogaru et al. (2009) and García-Rubio et al . (2016) find no effect of gender, while Doria (2010) find that women express more concern and perceive risks with tap water as higher.

The importance of high-quality tap water is best illustrated by what happens when the quality is poor. Examples from Norway include an outbreak of waterborne giardiasis in Bergen in 2004 after contamination of a municipal water supply ( Nygård et al. 2006 ), an outbreak of the gastrointestinal disease in Røros in 2007, sourced to groundwater waterworks ( Jakopanec et al. 2008 ), and E. coli contamination of a water holding pool in Askøy in 2019 ( Paruch et al. 2020 ). In the latter case, over 2,000 residents fell ill and two deaths were suspected to be associated with the contamination.

Norwegian citizen survey

Our main source of data is the Norwegian citizen survey which is carried out every second year by the Norwegian Agency for Public and Financial Management. The survey is sent in fall in even-numbered years and runs until spring in odd-numbered years. Each survey is then thoroughly documented in reports published by the agency ( Difi 2021 ). For ease of notation, we will refer to the year of the report when we date the surveys, i.e., we say the 2011 survey, rather than the 2010/11 survey and so on.

Satisfaction with tap water

An important take-away is that citizens are mostly very satisfied with their tap water, and the responses are also quite stable over time. In the first (2011) and last (2019) surveys, 54% give tap water the best grade, while 58–59% do so in the surveys in the intervening years. Moreover, the share giving the second-best grade is consistently in the mid to high 20s, while the share giving the lowest grade is well below 1% in all surveys. Hence, we also see that mean is in the area 6.2–6.3 in all surveys. Despite the high satisfaction, there is still meaningful variation in the data that allows us to conduct empirical test procedures.

Test result data

Test criteria for Norwegian drinking water

Source: Norwegian Institute of Public Health.

Descriptive statistics for water test results, measured as the percentage of the population with tap water that satisfied the test criteria in each year

When looking at the year-by-year descriptive statistics, we see that the numbers are quite stable for all criteria except for color. While the averages for the other ones are consistently in the mid to high 90s, the average for color varies from a low 78.4% in 2011 to a high 99.5% in 2019. The trend is positive, the numbers grow for each observation.

Although the numbers are consistently high and quite stable over time for E. coli , intestinal enterococci, and pH, the standard deviations show us that there is a sizable variation in the data, especially for pH. Hence, it is possible to conduct meaningful empirical analyses with these variables. However, since there is much more variation in the test results for color than the other criteria, this is the variable that is most likely to produce significant results in the empirical analyses.

Empirical specification

The vector containing demographic variables include a dummy for whether the respondent is male, and a set of dummies splitting the respondents into age categories. Due to anonymity concerns, we do not have access to the respondents’ exact age. We do not have any strong ex-ante expectations of the sign of the coefficients for these variables.

The vector with socio-economic characteristics consists of several variables. First, we include a dummy equal to one if the respondent voted for a left-leaning party in the last national election before the survey took place. The Norwegian left is almost completely dominated by the social democratic Labor Party and a moderate democratic socialist party which frequently cooperates with labor. Second, we include a dummy equal to one if the respondent is either married or lives together with his or her partner. Third, we use a dummy equal to one if the respondent has a degree from a college or university. Fourth, we include a dummy equal to one if the respondent is part of a household with a joint income of 1 million NOK (about 100,000 USD) or more. As for the demographic variables, we have no particular expectations for the sign of the coefficients for these variables.

Since our dependent variable is ordinal, we should also consider using an ordered probit model. As the number of categories in the dependent variable is rather large, the probit is not expected to make much of a difference. Hence, we favor the more simply interpreted OLS regression to the more technically refined ordered probit. Nonetheless, we will also report results from an ordered probit regression to show that the methods do not deviate substantially. Descriptive statistics for explanatory variables are provided in Table A1 in the Supplementary Material.

Robust standard errors in parentheses.

*** p <0.01, ** p <0.05, * p <0.1.

The first thing we note is the seemingly weak relationship between objective measures of water quality and citizen satisfaction. Of the four measures, three are far from reaching significance on any conventional level of significance, with coefficients that appear to be precisely estimated zeroes. Moreover, they also come out with an unexpected negative sign, although that is probably not worth putting much emphasis on.

Color does come out with the expected positive sign and the coefficient is also statistically different from zero. Despite the strong statistical significance, it is worth noting that the effect is of relatively modest size. An increase of one standard deviation in the share of the population with drinking water of a satisfactory color (27.36) is associated with an increase in satisfaction with the drinking water of about 0.05 or about 4.4% of the standard deviation for satisfaction (1.14).

It does make some sense from an intuitive perspective that color affects responses more than the other tests. While colored water is directly observable to consumers, marginal amounts of bacterium or deviations in pH are not. With a zero tolerance for both E. coli and intestinal enterococci, it is fully possible that deviations are reported, without the respondent ever being aware of it.

A second observation is that the general mood comes out with a strongly significant positive effect. An increase in the general mood by one standard deviation (0.88) is associated with an increase in satisfaction of about 0.38 or about 33% of the standard deviation for satisfaction. Hence, we see that the general mood explains a lot more of the variation in satisfaction with the drinking water than data for the objective quality.

When we turn to demographics, the first observation is that men are consistently more satisfied with the drinking water than women. A coefficient of about 0.05 translates into about 4.4% of the standard deviation for satisfaction. That is, the difference between men and women is the same as the effect of increasing the share of the population with water that satisfies the test criteria for color is very similar.

Second, we find some interesting age patterns. The oldest group (76 years and older) is significantly more satisfied with the drinking water than the younger groups. The difference is not only significant when comparing the group to the omitted control group (18–35 years), but also to any of the other age-groups. When compared to the control group, a coefficient of about 0.076 means the difference is in the area of 6.7% of the mean satisfaction. However, this does not mean that satisfaction improves steadily by age. Rather, both age-groups 36–45 and 46–55 years are significantly less satisfied with the drinking water than the youngest group. The difference for both groups compared to the youngest group is about −0.04, or approximately 3.5% of the standard deviation for satisfaction. The coefficient for the age-group 56–65 years is consistently negative, but smaller than for the two previous groups and mostly insignificant. For the age-group 66–75 years, the coefficient is positive, but consistently small and insignificant.

Hence, it seems the age effect takes the shape of a somewhat badly written U. The young are quite satisfied. The middle-aged are not so satisfied, the slightly old is in line with the young, and the seniors are even more satisfied. If we compare the groups that disagree most, age-groups 46–55, 76 years and older, the difference is around 0.12 or roughly 10% of the standard deviation for satisfaction.

The results for the socio-economic characteristics are a bit mixed. The coefficient for whether the respondent voted for a left-leaning party at the previous elections comes out as positive, but it is quite small and mostly insignificant. The richest model, which includes municipality-specific time trends, is borderline significant at the 10% significance level. The coefficient translates into about 1.7% of a standard deviation in satisfaction. Whether the respondent is married or not does not seem to affect the responses. The coefficient comes out as significant in all estimations but is never significant at any conventional level of significance.

Respondents with higher education are consistently less satisfied with the drinking water than those without a degree from a college or university. A coefficient of about −0.073 is equivalent to 6.4% of the standard deviation for satisfaction. For income, there is a trend that those in relatively high-income households are more satisfied with the drinking water than others. The coefficient is only borderline significant, though, and in some specification not even significant at the 10% level. The coefficient corresponds to about 2% of a standard deviation for satisfaction with the drinking water.

Inhabitants in Norway have access, almost always, to safe and high-quality tap water. It may have been somewhat colored earlier, but recently, color has also been very good. Satisfaction with tap water among Norwegian citizens, however, varies more, and somewhat unsettlingly, is not really related to objective measures of quality. Rather, satisfaction with tap water in Norway is mostly explained by the overall satisfaction with other things, such as schools, kindergartens, and museums. One may wonder if satisfaction with tap water impacts satisfaction with these factors. Age, education, income, political preference, and gender also factors into tap water satisfaction to various degrees. We can speculate on some mechanisms at play here. Some of those with higher education may be what we call connoisseurs or foodies and may be more sensitive to variations in quality. Also, household water treatment, for example with charcoal water filters, may be more common in high-income households.

One clear implication of our findings is that policy decisions related to tap water quality should not rely on how satisfied end users are with the tap water quality. Such decisions should rely on objective measures and other relevant aspects, such as socio-economic tradeoffs. Water supplies and water supply systems are costly to build and maintain. Despite the general affluence of the Norwegian society, parts of the public water supply systems are outdated. For example, subsequent to the outbreak of gastrointestinal disease in Røros, Norway, in 2007, several faults and problems with the distribution system were discovered, including 300 m of wooden pipes supplying the city center ( Jakopanec et al. 2008 ). The wooden pipes were laid down in 1942.

All relevant data are available from an online repository or repositories. ( https://dfo.no/sites/default/files/Fagomr%C3%A5der/Rapporter/2021/Innbyggerundersokelsen/Innbyggerundersokelsen-2021-Tabeller-med-alle-resultatene.xlsx and https://www.ssb.no/statbank/table/11786/ ).

The authors declare there is no conflict.

The questions were based on the general mood index with regard to churches and places of worship, museums, volunteer and sports associations, cultural life, air quality, noise, nursing homes, schools, and kindergartens. Among these, air quality and possibly noise may be related to factors impacting water quality. Leaving air quality and noise out of our mood index does not change our qualitative results.

Supplementary data

Journal of Water and Health Metrics

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  • J Dent (Shiraz)
  • v.16(3 Suppl); 2015 Sep

The Effectiveness of Home Water Purification Systems on the Amount of Fluoride in Drinking Water

Behrooz eftekhar.

a Dept. of Endodontic, School of Dentistry, Ahwaz Jondishapoor University of Medical Sciences, Ahwaz, Iran.

Masoume Skini

b Postgraduate Student, Dept. of Endodontic, School of Dentistry, Ahwaz Jondishapoor University of Medical Sciences, Ahwaz, Iran.

Milad Shamohammadi

Jaber ghaffaripour.

c DDS, School of Dentistry, Ahwaz Jondishapoor University of Medical Sciences, Ahwaz, Iran.

Firoozeh Nilchian

d Dental Students Research Center, Dept. of Dental Public Health, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran.

Statement of the Problem

Water purification systems for domestic use have drawn significant attention over the past few years. This can be related to the improvement of public health and concern for water contamination. 

The aim of this study was to evaluate whether home water purification systems eliminate the essential materials such as fluoride besides filtrating the heavy ions and other unwanted particles out of water.

Materials and Method

In this experimental study, six most frequently used commercial brands of water purifiers were evaluated and compared. Specimens were collected right before and after setting up the device, and 6 months later. Then, spectrophotometry (the Harrison device) was performed to compare fluoride clearance by each home water cleaner device.

Based on the data collected from all water purification devices in different locations, the amount of fluoride was significantly different before and right after using home water purifier and six months later ( p = 0.001 and p = 0.00, respectively).

The filtration of water significantly decreased its fluoride concentration. The fluoride content of purified water was approximately as much as zero in some cases.

Introduction

Fluoride is a natural element branched from Fluorine. This element can be found in all sorts of water and soil. Out of every kilogram of outer layer of earth, 0.3 gram is fluoride. Mineral waters have more amount of this element compared to other sources.( 1 )

About 60 years ago, Grand Rapids in Michigan State was the first city in which fluoride supplement was synthetically added to tap water. In US, adding fluoride to community water supplies of many cities has improved the oral health of millions of American citizens.( 2 )

Fluoridation of community water supplies is adding a specific amount of fluoride (0.7-1.2 ppm) to water in order to reduce the risk of dental caries. By 2002, almost 170 million Americans were provided with this privilege.( 3 )

Since most of the systemic fluoride is provided through tap water to population, many policies have been established to add fluoride to community water regarding its benefits for teeth and bones.( 4 )

In regions and countries that do not have water-fluoridation technology, there are natural supplements as previously mentioned. For example, Iran has many mineral water supplies that contain considerable amounts of fluoride. Amount of fluoride in natural mineral waters depends on weather conditions; the warmer the weather is, the higher the amount of fluoride can be detected. Mineral waters in southern regions that have warmer weather contain more fluoride. In Iran, the highest amount of fluoride has been found in southeast and northeast areas.

Water purification systems for domestic use have drawn much of attention over the past few years. This can be related to improvement of public health and concerns for water contamination. There are several types of home water purification systems that can be categorized into 3 different groups( 5 ) as filtered systems, systems using UV irradiation, and ion-exchange systems.

The aim of this study was to find out whether domestic water purification systems could eliminate the essential materials such as fluoride besides filtrating the heavy ions and other unwanted particles out of water.

In this study, 6 frequently used commercial brands of water purifiers in Ahwaz were compared. The commercial brands evaluated in the current study were CCK (Ceramic and Ceramic/Carbon Cartridges ; RTX-TS DLM filters, Korea), Soft Water (Ceramic Candles; Alpine TJ Series filters, W9332420, USA), Alkusar (Special media cartridges filters; PRB50-IN, USA), Puricom (Special media cartridges filters; Watts 4.5" x 10" Dual Housing, Korea), Water Safe (Granular Carbon Cartridges filters; LCV (Lead, Cysts, VOC's) (Carbon Block Filter Cartridges, Australia), and Aquafresh (Sediment String-Wound; Poly Spun and Pleated Washable Cartridges filters, K5520, USA). The main drinking water supply for Ahwaz is provided by governmental companies. After making arrangement with certain companies that supported these brands, the devices were setup in 6 different regions of Ahwaz. Samples were collected before and right after setting up the device. To reduce the errors and elevate the accuracy of the module, 5 samples were taken from each device. Another sample was collected from each single device 6 months later. A total of 64 samples were collected including 32 unfiltered (control) and 32 filtered samples of tap water (experimental) from 6 regions in Ahwaz. Fluoride sampling kits (Spands; EW-99574-08Hach ® Test Kits, USA) were used to test the amount of fluoride in sample waters. Samples were all collected in polyethylene sampling containers and were then coded. Spectrophotometry (AvaSpec-ULS2048L- USB2 UARS spectrometer, USA) was performed. In order to measure the characteristics of individual molecules, a mass spectrometer converted them to ions so that they could be moved about and manipulated by external electric and magnetic fields.

Atmospheric pressure was around 760 torr (mm of mercury). The pressure under which ions may be handled is roughly 10 -5 to 10 -8 torr (less than a billionth of an atmosphere). By varying the strength of the magnetic field, ions of different mass can be focused progressively on a detector fixed at the end of a curved tube and also under a high vacuum.

Latin alphabetic words were used to code each commercial device. Numbers were used for samples obtained before and after setting the device.( 6 )

The results were analyzed by using paired sample t-test, with alpha (ɑ) set at 0.05.

The amount of fluoride in water before and after using six brands of water purifier device is summarized in Table 1 .

The amount of fluoride before and after installing water purifier devices

Based on the data gathered from all water purification devices set in different regions, the level of fluoride was significantly different before and after using home water purifier ( p = 0.001). It was found that home water purifiers nearly eliminated fluoride from tap water. Table 2 represents the results of t-test.

Comparison of different study groups with t-test

* p< 0.05 is statistically significant.

Another round of sampling was done 6 months later from the same filters of home water purifier. Details are illustrated in Table 3 and 4.

The amount of fluoride in tap water after 6 months of using a water purification filter

Comparison of the study groups after six mounts with t-test

Fluoride absorption is mostly systemic or local; systemic absorption occurs through eating the element with food, water or fluoride pills, and local absorption by toothpastes and other fluoride-containing hygienic products. In many countries, the highest supply for fluoride absorption is systemic absorption through water consumption.( 6 ) In early 20 th century, the first attempts were made to fluoridate public water supplies, which eventually led to 40% decrease of dental caries in the target population.( 7 )Introduction of water fluoridation in the 1950-1960 and fluoride-containing dental products in the 1970 changed the situation. The main sources of fluoride in established market economies (EME) are drinking water, fluoridated salt, foods and beverages, baby cereals and formulas, fluoride supplements, toothpastes, mouth-rinses, and topical fluorides. Additionally, fluoride in water has a diffusion or halo effect; which means that the drinks and foods manufactured in fluoridated areas are also available to whole population including the residents of non-fluoridated areas.

Although adding fluoride to almost all oral hygienic products has restricted the effect of fluoride water (Halo effect), it is still common to fluoridate the city water supply.( 6 ) In many areas of the world, there is no systematic plan for fluoridation of community water and only the natural sources supply it. Therefore, sometimes the hardness of water and aggregation of different and sometimes poisonous elements drive the population to use bottled water or use home purification devices.

The findings of the present study revealed that all the 6 devices reduced the fluoride in tap water and most of them nearly eliminated it. Different home purification devices have been marketed each of which is claimed to eliminate certain kinds of elements from water.( 9 ) JK Mwabi et al. (2011) used 4 different filters to reduce the hardness and chemical contamination of water in poor villages in Africa, and reported that all of the four filters reduced the fluoride significantly. Bucket filter had the most significant effect and reduced fluoride element 99.9%. These results also indicated that fluoride was the most reduced element of all. Likewise, silver-impregnated porous pot (SIPP) filter reduced 90%-100% of elements.

Clasen et al. ( 5 ) in their study reported that 3 different home purification systems ,the ceramic candle gravity filter, iodine resin gravity filter, and iodine resin faucet filter, reduced bacterial contamination by four logs and decreased ions such as fluoride and arsenic, as well.

Moreover, there are certain methods to reduce the excessive amount of fluoride in the water. One of the best-known methods is absorption technique.( 7 ) Evaluation of 6 different commercial water purifiers has not been done in any other study; therefore, there is no similar study to compare the results exactly. More evaluations are suggested to be performed on home water purification systems, and more strategies should be devised to preserve the essential elements of tap water.

The current study found considerable differences between the amount of fluoride before and after filtration with home purification device; that is filtration significantly decreased the fluoride concentration even as much as 100% in some cases.

Conflict of Interest: None declared

Tap Water Quality Degradation in an Intermittent Water Supply Area

  • Open Access
  • Published: 25 February 2022
  • volume  233 , Article number:  81 ( 2022 )

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  • Bijay Man Shakya 1 , 2 ,
  • Takashi Nakamura   ORCID: orcid.org/0000-0002-4080-3583 2 ,
  • Sadhana Shrestha 1 , 3 , 4 ,
  • Sarad Pathak 1 ,
  • Kei Nishida 2 &
  • Rabin Malla 1  

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Decentralized tap water systems are an important drinking water source worldwide. A good quality, high-pressure continuous water supply (CWS) is always the target of any urban settlement. However, tap water in some areas are reported with deteriorated water quality even though treated well before supplying. Such deterioration of tap water quality is reported widely from areas with low water availability and in economically poor countries where water are supplied intermittently (IWS). This study focuses in identifying tap water quality in IWS and causes of water quality degradation using nitrate-nitrogen (NO 3 -N) as an indicator and stable isotopes of hydrogen (δD) as tracer. Nine water reservoirs and ninety municipal tap water (ten per reservoir) samples were collected during the wet (June–September) and dry (November–February) seasons in the Kathmandu Valley (KV), Nepal. Ten percent of the tap water samples exhibited higher NO 3 -N than those of their respective reservoirs during the wet season, while 16% exhibited higher concentrations during the dry season. Similarly, the isotopic signatures of tap water exhibited 3% and 23% higher concentrations than those of their respective reservoirs during the wet and dry seasons, respectively. Coupling analysis between NO 3 -N and δD demonstrates close connection of groundwater and tap water. The results indicate groundwater intrusion as the primary component in controlling tap water quality variations within the same distribution networks during IWS. Meanwhile, the obtained results also indicate probable areas of intrusion in the KV as well as usefulness of δD as a tool in the assessment of tap water systems.

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1 Introduction

Maintaining safe drinking water for growing populations is a major global issue. In addition, anthropogenic impacts on water sources and climate change have raised serious concerns regarding drinking water resources (IPCC, 2008 ). The construction of continuously available and easily accessible water sources, their maintenance, and sustainability are continually being developed to cope with drinking water scarcity. Therefore, decentralized municipal tap water systems have served as a critical component of safe and convenient drinkable water (Howard & Bartram, 2003 ).

Although municipal tap water networks are safe, they are vulnerable to artificial (pressure loads, management, and replacement) and natural changes (underground stresses, earthquakes, disasters) that can cause dislocations and ruptures (Chandra et al., 2016 ; Wols et al., 2014 ). Losses of 5–35% of water (Lambert et al., 2014 ) through ruptures in municipal tap water networks are inevitable which can reach up to 50% in low-income countries (Dudley & Stolton, 2003 ). These ruptures and losses have a significant effect of water leakage faced by areas with continuous water supply (CWS) (24 h) wherein the water supply is steadily under high pressure. On the other hand, intermittent water supply (IWS) strategy with limited supply per day (< 24 h) to per week (1–3 h in a week) has been adopted as a counter measure to cope with water shortages and losses in economically poor countries (van den Berg & Danilenko, 2011 ; WHO & UNICEF, 2000 ). However, chemical and microbiological contamination has been found to be significantly higher during IWS than during CWS (Erickson et al., 2017 ; Kumpel & Nelson, 2014 ).

Previous studies have reported that contamination of the tap water distribution network-harbored material (DNHM) is caused by chemical disintegration and microbiological re-growth (Liu et al., 2017 ). Disintegration and re-growth are even higher in IWS settings during periods of no supply (Coelho et al., 2003 ). In addition, the occurrence of transient low or negative pressure mechanisms in the distribution pipes during IWS is ubiquitous during transport (Fontanazza et al., 2015 ; Kumpel & Nelson, 2014 ; van den Berg & Danilenko, 2011 ). Presence of any ruptures in the distribution network thus acts as a major gateway for subsurface backflow and foreign water intrusions. These intrusions ultimately contribute to the degradation and contamination of drinking water quality, which is also related to the surrounding groundwater conditions (Grimmeisen et al., 2016 ). Groundwater, which is in close contact with municipal drinking water pipes, is reported to be contaminated with both chemical and microbiological contaminants, especially in developing countries (Nakamura et al., 2012 ; Shakya et al., 2019b ; Shrestha et al., 2014 ; Umezawa et al., 2009 ), resulting in a higher likelihood of the deterioration of tap water quality caused by backflow into pipe network. Any changes in the tap water quality compared with reservoirs and nearby contaminated groundwater might indicate the tap water quality variations within the same network. Since NO 3 -N in groundwater is considered an indicator of contaminations, studies focusing on determination of the tap water quality especially from NO 3 -N create a concept on the drinking water situation and its possible risk (Schullehner et al., 2018 ). However, chemical and microbial tracers alone may not be reliable for defining tap water degradation, whether it is from the DNHM or intrusions. Meanwhile, the use of oxygen (δ 18 O-H 2 O) and hydrogen (δD) isotopes in water has been advantageous for identifying various types of mixing in diverse hydrological studies (Craig, 1961 ; Gonfiantini et al., 1998 ). The fractionation of the isotopic signatures (δD and δ 18 O-H 2 O) of water caused by natural processes (evaporation or condensation) is identical and can be identified. The distinct isotopic values of various water sources, as well as the properties of the isotopic tracers, have aided a wide variety of mixing studies and have been used advantageously for hydrological studies (Nakamura et al., 2016 ; Yang et al., 2012 ). Additionally, stable isotopes especially δD is unaffected by the pre-treatment processes. With all the advantages, stable isotopes have been used to determine the water dynamics in urban areas with CWS (Bowen et al., 2007 ; de Wet et al., 2020 ; Ehleringer et al., 2016 ; Jameel et al., 2018 ; Tipple et al., 2017 ; Zhao et al., 2017 ). As CWS does not experience foreign intrusions (Erickson et al., 2017 ), the dependency on isotopic signatures for tap water conditions and dynamics in an IWS setting presents challenges. Thus, the isotopic signatures coupled with chemical parameters among the water sources might be beneficial for understanding and investigating municipal tap water chemical contamination in urban areas facing IWS.

In this study, we investigated the municipal drinking water system of the Kathmandu Valley (KV) in Nepal. Similar to other cities in South Asia facing IWS (including Delhi, Dhaka, and Karachi), the KV faces higher intermittent supplies of all drinking water systems (McIntosh, 2003 ). Most of the residents in the KV experience an IWS for 2–4 h/week (Shrestha et al., 2017 ). More specifically, they experience intermittent supplies three or fewer times per week for two or fewer hour each time (Guragai et al., 2017 ). Despite better access to drinking water than in rural areas of Nepal, people in the KV experience safe drinking water problems in terms of both quality and quantity (Koju et al., 2015 ; Thapa et al., 2017 , 2019 ; Udmale et al., 2016 ; Warner et al., 2008 ). Furthermore, the study area is often reported with the aging distribution network pipes and management (KUKL, 2019 ). The coupled use of NO 3 -N as an indicator of contamination and isotopic signatures in areas severely affected by water shortages and intermittent distribution presents a new perspective on the diversity of tap water chemical contamination status in urban areas. Therefore, we highlighted the seasonal tap water NO 3 -N contamination, its possible causes in the KV IWS, and the use of isotopic signatures as a tool in tracking the area of contamination from the distribution reservoir to the end users in the urban area.

2 Materials and Methods

2.1 study area.

The KV is located in the foothills of the Himalayas and is an isolated closed intermountain basin. The basin extends from 27°32′34″ to 27°49′11″ N and from 85°11′10″ to 85°31′10″ E (Fig.  1 ). The valley covers an area of 664 km 2 , with elevations ranging from 1212 to 2722 m above sea level. The water resources in the valley are rainfall-dependent. The KV receives 80% of its annual rainfall during the monsoon (wet) season (June–September), 14% during the pre-monsoon season (March–May), and 6% during the dry season (November–February) (Prajapati et al., 2021 ).

figure 1

Geographical boundary of the Kathmandu (KTM) Valley, with KUKL service areas shown in blue. Areas outside of the blue highlighted regions are not serviced by KUKL. The dashed line represents tap water from their respective reservoirs

The sole water supply utility, Kathmandu Upatyaka Khanepani Limited (KUKL), has difficulties covering the annual drinking water demand for a population of 2.5 million people. According to KUKL ( 2021 ), the total demand for drinking water in 2019 reached 470 million liters per day (MLD); however, the provider was only able to provide 120 MLD during the wet season and 108 MLD during the dry season. The water supply demand is managed by a long intermittent supply, while the deficits are covered by groundwater supplies and other water vendors. Deep groundwater extracted from spatially distributed aquifers reaching the depths of 75–300 m is used for the drinking water supply by KUKL, while shallow groundwater at depths of up to 50 m is commonly used for local water use.

2.2 Tap Water and Reservoir Sample Collection

In this study, 198 samples were collected from around the KV during 2018–2019 (Fig.  1 ). Spatially distributed treated drinking water reservoirs in nine service areas, as well as 10 successive municipal taps (at the consumer end) within 3–5 km of the reservoir, were sampled during two consecutive seasons, i.e., wet (June–September 2018) and dry (November 2018–February 2019). Ninety-nine samples were collected per season. Tap water samples were collected 5–10 min after the supply started during the intermittent cycle. In case of reservoirs, samples were collected from the storage tanks. The samples were collected in 120 ml airtight high-density polyvinyl chloride (PVC) bottles. The samples were transferred from the collection area stored in a cooler bag with no preservatives added, then stored at − 4 °C. The samples were then transferred to the Interdisciplinary Centre for River Basin Environment at the University of Yamanashi (ICRE-UY) in Japan for further analysis.

The groundwater data used for comparison with the tap water data were adopted from the data previously reported by Shakya et al., ( 2019a , b ).

2.3 Laboratory Analyses

The hydrogen (H) and oxygen (O) stable isotopic compositions and the chemical parameters of the samples were analyzed in the laboratory at ICRE-UY. The dual isotopic signatures were analyzed using cavity ring-down spectroscopy (L1102-i, Picarro, Santa Clara, CA, USA). The abbreviations δD and δ 18 O-H 2 O relative to Vienna Standard Mean Ocean Water (V-SMOW) are used to represent the stable isotopes of hydrogen and oxygen in water, respectively. All isotopic ratios are expressed in per mil format (‰), as shown in Eq.  1 :

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where N is the atomic mass of the heavy isotope of the element, and E and R are the ratios of the heavy to light isotopes ( 2 H/ 1 H or 18 O/ 16 O). The measured analytical error of the equipment was 0.5‰ for δD and 0.1‰ for δ 18 O-H 2 O.

The elemental concentrations of the samples (NO 3 -N) were measured using ion chromatography (ICS-1100, Dionex, USA), with an analytical error of 5%.

2.4 Statistical Analyses

Mapping of the analyzed isotopic signatures and chemical parameters was performed using ArcMap version 10.3.1 (Esri Inc., USA). A paired t -test was performed to identify the temporal variations among the samples—based on p -value of 0.05—using the Statistical Package for Social Studies version 20 (SPSS Inc., Chicago, IL, USA).

3 Results and Discussion

Tables 1 and 2 list the statistics of the NO 3 -N concentrations and stable isotopic signatures of the water samples (δD and δ 18 O-H 2 O) obtained from the drinking water reservoirs and tap water in the KV, respectively.

3.1 Nitrate Concentrations of the Reservoir and Tap Water

The NO 3 -N concentrations varied spatially and temporally (wet and dry seasons) (Fig.  2 ). NO 3 -N ranged from 0.03 to 8.11 mg N/L during the wet season and from 0.01 to 1.88 mg N/L during the dry season. The average NO 3 -N concentration during the wet season was higher (0.54 mg N/L) than during the dry season (0.37 mg N/L). Statistically, the values were found to differ significantly ( p  < 0.05) between the two seasons (Table 3 ), even though the NO 3 -N concentrations in some locations were similar. Similarly, the NO 3 -N concentrations of the reservoirs ranged from 0.18 to 0.84 mg N/L during the wet season and from 0.05 to 0.57 mg N/L during the dry season (Table 2 ). The concentrations of NO 3 -N in both the reservoir and tap water samples were below the permissible limit of 10 mg N/L specified by both the World Health Organization (WHO) and the Nepal Drinking Water Quality Standard (NDWQS). However, Schullehner et al. ( 2018 ) suggests that when conforming with the permissible limit, the higher concentration of NO 3 -N during the dry season possesses risk to the water users.

figure 2

Reservoir, tap water, and groundwater NO 3 -N concentrations. Cross mark plotted at the right of each season represents groundwater NO 3 -N (mg/l) concentrations from the nearby tap water location during each consecutive season. Groundwater data are acquired from Shakya et al. ( 2019b )

In general, the water quality of the distribution tank and tap water must be identical. Although chloride (Cl − ) is considered to be a major conservative tracer, Cl − was not considered in this study, as no free chlorine was measured from the samples. However, the NO 3 -N concentrations of the tap water and reservoir samples exhibited differences (Fig.  2 ). Compared with their respective reservoirs, 10% of the tap water samples had higher NO 3 -N concentrations than the reservoirs during the wet and dry seasons, while 16% of the tap water samples had higher NO 3 -N concentrations during the dry season. Anamnagar (dry 2), Sainbu (dry 3), Bode (wet 1, dry 3), Sundarighat (dry 2), Balaju (wet 2, dry 1), Panipokhari (wet 1), and Simbhanjyang (wet 6, dry 5) exhibited local contamination. Such areas of contamination are generally observed due to DNHM in IWS, while little or no contamination is observed in areas with CWS (Erickson et al., 2017 , Kumpel and Nelson, 2014 ). In addition to DNHM, backflow and/or re-suspension of particulate matter induced by low and transient negative pressure during transfer is the governing contamination mechanism (Erickson et al., 2017 ; Kumpel and Nelson, 2014 ; van den Berg & Danilenko, 2011 ). Similarly, in previous studies (Nakamura et al., 2014 ; Shakya et al., 2019b ; Warner et al., 2008 ), groundwater in the KV was determined to be contaminated by chemical and microbiological components due to the leaky septic systems. Although a time series analysis was not performed, the shifts in NO 3 -N concentrations away from the reservoir and close to the groundwater indicate occurrence of various degrees of NO 3 -N contaminations from groundwater which is spatially varied by heterogenous anthropogenic nitrogen loading in the subsurface (Nakamura et al., 2014 ; Shakya et al., 2019b ). As shown in Fig.  2 , the deflections of tap water concentrations from those of the reservoirs were higher during the dry season, and higher NO 3 -N concentrations were observed during the wet season. Similar results regarding the contamination of stored piped water have been reported in the KV during the dry season with a larger supply gap (Shrestha et al., 2013 ). Although precise conclusions could not be drawn from the NO 3 -N concentrations alone, assumptions can be made where the increment in groundwater level and heterogeneously distributed NO 3 -N concentration during the wet season might have created such variations. The assumptions follow a study of India and Panama (Erickson et al., 2017 ), where the degree of intrusion was higher in areas with a lower supply, which can be used to explain the higher NO 3 -N deflection during the dry season in the KV. Additionally, high demand and extraction during periods of low-pressure tap water play a vital role in the intrusion (Fontanazza et al., 2015 ). Compared with the wet season, drinking water demand and extraction in the KV are higher during the dry season (KUKL, 2021 ), causing contamination backflow in numerous locations. However, 2% of the samples during the dry season and 7% during the wet season had NO 3 -N concentrations lower than those of the Sundarighat and Balaju reservoirs (Fig.  2 ). Such conditions wherein the tap water has lower concentrations of NO 3 -N than the reservoirs and lower occurrences of contamination are presumed to be caused by mixing with rainwater having lower NO 3 -N concentration.

3.2 Stable Isotopes of Reservoir and Tap Water

The δD and δ 18 O-H 2 O of the tap water ranged from − 66.23 to − 52.1‰ and from − 9.48 to − 7.81‰, respectively, during the wet season, and ranged from − 67.3 to − 46.1‰ and from − 9.38 to − 7.33‰, respectively, during the dry season. Seasonally, δD exhibited no significant changes (> 0.05), while δ 18 O-H 2 O had significant variations (< 0.05). Similarly, the reservoir samples ranged from − 64.09 to − 51.37‰ and from − 9.08 to − 7.76‰, respectively, during the wet season, and ranged from − 51.2 to − 68.0‰ and from − 9.33 to − 7.56‰, respectively, during the dry season (Tables 1 and 2 ). The isotopic ranges were considerably higher during the dry season than during the wet season (Fig.  2 ). Among the service areas, Bode had the lightest isotopic values, while Bansbari had the heaviest water isotopic values during both the dry and the wet seasons. A graph of δD vs. δ 18 O-H 2 O (Fig.  3 ) shows the spatial and temporal variations in the isotopic signatures. As reported by Wet et al. ( 2020 ), the degree of evapoconcentration or groundwater intrusion that is recharged under different climatic condition can cause variations in the tap water composition. Compared with the global (GMWL) and local (LMWL) meteoric water lines, which are defined as δD = 8*δ 18 O-H 2 O + 10 (Craig, 1961 ) and δD = 8.1*δ 18 O-H 2 O + 12.3 (Gajurel et al., 2006 ), respectively, no evidence of evaporation was observed. As the isotopic signatures of deep groundwater are constant throughout the entire year (Chapagain et al., 2009 ), cluster of the isotopic signatures from reservoirs during the wet season shows the influence of local precipitation during the pre-treatment. However, the contribution of rainfall during pre-treatment is less likely to occur. Additionally, the valley is a closed basin and no intra-basin water transport for tap water network occurred until the study was performed; the variations in the seasonal isotopic signatures are affected by spatially distributed aquifer affected by the local rainfall during the wet season. The isotopic signatures of the tap water sources varied spatially, as their sources are recharged at various altitudes (West et al., 2014 ; Wet et al., 2020 ; Zhao et al., 2017 ). The spatiotemporal variations therefore represent the use of isotopically distinguishable local water sources (Shakya et al., 2019a ).

figure 3

Plot of δD vs. δ 18 O-H 2 O of the tap water and reservoir samples compared with the global meteoric water line (GMWL) (Craig, 1961 ) and local meteoric water line (LMWL) (Gajurel et al., 2006 )

We also compared the δD composition of the tap water samples with that of the reservoirs and the groundwater (Fig.  4 ). For a threshold of 3‰, 28% of the isotopic values of the tap water samples were displaced away from the values of the reservoirs during the dry season, while 5% were displaced during the wet season. Because evapoconcentration does not cause isotope fractionation, the tap water variations were likely due to groundwater contamination during the drinking water transfer. As with NO 3 -N, the spatial isotopic distributions of the tap water sample varied with those of the on-site groundwater (Fig.  4 ). In addition, the tap water anomalies varied from the respective reservoirs but were similar to the respective on-site shallow groundwater isotopic signatures. Temporally, the δD values were more clustered during the wet season than the dry season The monsoon rainfall accounts for a large part of the groundwater in the KV (Prajapati et al., 2021 ), and the δD values indicate the rainfall control on the tap water network in the KV.

figure 4

Isotopic signatures of the tap water samples and those of their respective reservoirs and on-site groundwater. Cross mark plotted at the right of each season represents groundwater δD (‰) concentrations from the nearby tap water location during each consecutive season. Groundwater data are acquired from Shakya et al. ( 2019a )

3.3 Comparison of δD and NO 3 -N

The similarities and anomalies observed in the tap water samples provide information on intrusion contamination within the tap water network. Coupled techniques have helped to determine the source and mechanism of various hydrological and hydrogeochemical processes (Umezawa et al., 2009 ). No significant correlations in spatial variations were observed between NO 3 -N and δD in the samples, a phenomenon that might be attributed to changes in the rate of transfer and nearby groundwater condition. In addition, a Pearson correlation indicates similarities between the deflected NO 3 -N and δD values. Although only 16% of the samples had higher NO 3 -N values than those of the reservoirs during the dry season, similar behaviors were observed for the variations between NO 3 -N versus δD and were significantly related ( p -value > 0.05). This statistical similarity between higher NO 3 -N and δD values reflects intrusions from nearby groundwater sources. Comparisons of the groundwater isotopic values and those of the tap water (Fig.  4 ) suggest advantages in identifying possible intrusion areas. In contrast, the coherence of the NO 3 -N and δD values decreased to < 10% during the wet season, with no significant correlation ( p -value < 0.05). This implies the possibilities of rainfall dominated groundwater intrusions creating difficulties in disparity between groundwater and tap water from reservoirs. Uncertainty remains regarding those tap water samples with lower NO 3 -N values and similar δD as of the groundwater. This uncertainty may be due to the amount of rainfall infiltration and anthropogenic nitrate loading to the groundwater; however, further mixing analyses are required to confirm this. Although few of the anomalies coincided (i.e., 20 samples for both NO 3 -N and δD), the obtained results indicate that δD can be used as a potential indicator in identifying the tap water leakage and groundwater intrusions.

Despite the tap water dynamics caused by the use of various water sources (Bowen et al., 2007 ; de Wet et al., 2020 ; Tipple et al., 2017 ; Zhao et al., 2017 ), the contamination from the groundwater intrusion was responsible for the variations in the isotopic signatures of the reservoirs and tap water samples. The use of coupled indicators NO 3 -N and δD provided a clear picture of nearby groundwater intrusions. Furthermore, comparisons of NO 3 -N and δD made between tap water and groundwater signal the locations of groundwater intrusions and backflow whether nearby or far from the end users within tap water network. This also helps the management to identify the areas for immediate maintenance of tap water network. Although the paper lacks information on pressure control during the water supply and water demands, due to constraints in continuous data measurement, this study presents baseline data that can be used to widen the study of tap water using stable isotopes, particularly in developing nations facing IWS.

4 Conclusions

Losses of the municipal supplied water through ruptures and breakages in the tap network during the high pressurized CWS is the major urban water supply issue. However, negative pressure developed during the IWS not only creates water losses but also results in contaminations due to intrusions of the groundwater through the ruptures during water transport from the reservoir to the tap. This study showcased the contamination status especially NO 3 -N contamination in the municipal distributed tap water and the cause of contaminations in an area facing IWS. Even when the NO 3 -N concentrations were within established drinking water quality standards, a comparative analysis of the tap water, reservoirs, and the surrounding groundwater indicates that up to 10% of NO 3 -N from tap water samples were not similar to the reservoirs during the wet season, while the same increased to 16% during the dry season. Those tap water with difference NO 3 -N values were found to be close to the groundwater, indicating the possibilities of intrusions. Similarly, the stable isotopic signatures of the tap water samples also varied compared with their respective reservoirs, irrespective of any fractionation caused by evaporation showing 5% variation during the wet and 28% during the dry season. The differences between wet and dry season indicates the control of the rainwater even in the tap water networks of the area with IWS. The positive correlation between NO 3 -N and δD indicates groundwater intrusion as one of the prime causes of water quality deterioration within the same distribution area (caused by the low or negative pressure either nearby or far from the end users). Furthermore, this study also depicts the use of δD as a possible tracer for evaluating the tap water conditions when locating the intrusions in the area with IWS.

Despite the fact that pressure control and the water supply vary depending on the distribution network and water demands, we were unable to associate pressure control information with continuous monitoring. Additionally, other conservative hydrochemical and microbiological tracers and pressure information, which can serve as strong supporting information in IWS studies, are not included due to the lack of data availability and will be including as the future task. Nevertheless, this study provided insights into the seasonal variations in NO 3 -N concentrations in the area with IWS (KV as an example) and causes of NO 3 -N contaminations using δD as a tracer. The tap water variations due to possible foreign water interactions and differences of δD from reservoir to the tap mentioned in this study are expected to establish the baseline in creating precise tap water studies, particularly in low-income countries.

Data Availability

The excel file of analyzed tap water data and reservoir water that supports the findings of this study are all available in repository “figshare” and cited as Shakya et al. ( 2021 ).

Data are presented in “Tap water contamination status of an intermittent water supply_.xlsx.” The tap water data are presented in Table 1 while the reservoir water sample data are presented in Table 2 .

Code Availability

Not applicable.

Shakya, B., Nakamura, T., Shrestha, S., Pathak, S., Nishida, K., Malla, M. (2021).Tap water contamination status of an intermittent water supply_.xlsx. figshare. Dataset. 10.6084/m9.figshare.16584113.v1

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This research was carried out in the framework of the Coordinated Research Project (CRP) F33024 – “Isotope Techniques for the Evaluation of Water Sources for Domestic Supply in Urban Areas” of the International Atomic Energy Agency (IAEA), and was partly funded by Grants-in-Aid for Scientific Research (KAKENHI No. 20H02285) and Accelerating Social Implementation for SDGs Achievement (aXis: JPMJAS2005) Japan. We would also like to thank the Science and Technology Research Partnership for Sustainable Development (SATREPS), Japan International Cooperation Agency (JICA), and Japan Science and Technology (JST) for their financial support.

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Shakya, B.M., Nakamura, T., Shrestha, S. et al. Tap Water Quality Degradation in an Intermittent Water Supply Area. Water Air Soil Pollut 233 , 81 (2022). https://doi.org/10.1007/s11270-021-05483-8

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Drinking water quality assessment and its effects on residents health in Wondo genet campus, Ethiopia

  • Yirdaw Meride 1 &
  • Bamlaku Ayenew 1  

Environmental Systems Research volume  5 , Article number:  1 ( 2016 ) Cite this article

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Water is a vital resource for human survival. Safe drinking water is a basic need for good health, and it is also a basic right of humans. The aim of this study was to analysis drinking water quality and its effect on communities residents of Wondo Genet.

The mean turbidity value obtained for Wondo Genet Campus is (0.98 NTU), and the average temperature was approximately 28.49 °C. The mean total dissolved solids concentration was found to be 118.19 mg/l, and EC value in Wondo Genet Campus was 192.14 μS/cm. The chloride mean value of this drinking water was 53.7 mg/l, and concentration of sulfate mean value was 0.33 mg/l. In the study areas magnesium ranges from 10.42–17.05 mg/l and the mean value of magnesium in water is 13.67 mg/l. The concentration of calcium ranges from 2.16–7.31 mg/l with an average value of 5.0 mg/l. In study areas, an average value of sodium was 31.23 mg/1and potassium is with an average value of 23.14 mg/1. Water samples collected from Wondo Genet Campus were analyzed for total coliform bacteria and ranged from 1 to 4/100 ml with an average value of 0.78 colony/100 ml.

On the basis of findings, it was concluded that drinking water of the study areas was that all physico–chemical parameters. All the Campus drinking water sampling sites were consistent with World Health Organization standard for drinking water (WHO).

Safe drinking water is a basic need for good health, and it is also a basic right of humans. Fresh water is already a limiting resource in many parts of the world. In the next century, it will become even more limiting due to increased population, urbanization, and climate change (Jackson et al. 2001 ).

Drinking water quality is a relative term that relates the composition of water with effects of natural processes and human activities. Deterioration of drinking water quality arises from introduction of chemical compounds into the water supply system through leaks and cross connection (Napacho and Manyele 2010 ).

Access to safe drinking water and sanitation is a global concern. However, developing countries, like Ethiopia, have suffered from a lack of access to safe drinking water from improved sources and to adequate sanitation services (WHO 2006 ). As a result, people are still dependent on unprotected water sources such as rivers, streams, springs and hand dug wells. Since these sources are open, they are highly susceptible to flood and birds, animals and human contamination (Messeret 2012 ).

The quality of water is affected by an increase in anthropogenic activities and any pollution either physical or chemical causes changes to the quality of the receiving water body (Aremu et al. 2011 ). Chemical contaminants occur in drinking water throughout the world which could possibly threaten human health. In addition, most sources are found near gullies where open field defecation is common and flood-washed wastes affect the quality of water (Messeret 2012 ).

The World Health Organization estimated that up to 80 % of all sicknesses and diseases in the world are caused by inadequate sanitation, polluted water or unavailability of water (WHO 1997 ). A review of 28 studies carried out by the World Bank gives the evidence that incidence of certain water borne, water washed, and water based and water sanitation associated diseases are related to the quality and quantity of water and sanitation available to users (Abebe 1986 ).

In Ethiopia over 60 % of the communicable diseases are due to poor environmental health conditions arising from unsafe and inadequate water supply and poor hygienic and sanitation practices (MOH 2011 ). About 80 % of the rural and 20 % of urban population have no access to safe water. Three-fourth of the health problems of children in the country are communicable diseases arising from the environment, specially water and sanitation. Forty-six percent of less than 5 years mortality is due to diarrhea in which water related diseases occupy a high proportion. The Ministry of Health, Ethiopia estimated 6000 children die each day from diarrhea and dehydration (MOH 2011 ).

There is no study that was conducted to prove the quality water in Wondo Genet Campus. Therefore, this study is conducted at Wondo Genet Campus to check drinking water quality and to suggest appropriate water treated mechanism.

Results and discussions

The turbidity of water depends on the quantity of solid matter present in the suspended state. It is a measure of light emitting properties of water and the test is used to indicate the quality of waste discharge with respect to colloidal matter. The mean turbidity value obtained for Wondo Genet Campus (0.98 NTU) is lower than the WHO recommended value of 5.00 NTU.

Temperature

The average temperature of water samples of the study area was 28.49 °C and in the range of 28–29 °C. Temperature in this study was found within permissible limit of WHO (30 °C). Ezeribe et al. ( 2012 ) reports similar result (29 °C) of well water in Nigeria.

Total dissolved solids (TDS)

Water has the ability to dissolve a wide range of inorganic and some organic minerals or salts such as potassium, calcium, sodium, bicarbonates, chlorides, magnesium, sulfates etc. These minerals produced un-wanted taste and diluted color in appearance of water. This is the important parameter for the use of water. The water with high TDS value indicates that water is highly mineralized. Desirable limit for TDS is 500 mg/l and maximum limit is 1000 mg/l which prescribed for drinking purpose. The concentration of TDS in present study was observed in the range of 114.7 and 121.2 mg/l. The mean total dissolved solids concentration in Wondo Genet campus was found to be 118.19 mg/l, and it is within the limit of WHO standards. Similar value was reported by Soylak et al. ( 2001 ), drinking water of turkey. High values of TDS in ground water are generally not harmful to human beings, but high concentration of these may affect persons who are suffering from kidney and heart diseases. Water containing high solid may cause laxative or constipation effects. According to Sasikaran et al. ( 2012 ).

Electrical conductivity (EC)

Pure water is not a good conductor of electric current rather’s a good insulator. Increase in ions concentration enhances the electrical conductivity of water. Generally, the amount of dissolved solids in water determines the electrical conductivity. Electrical conductivity (EC) actually measures the ionic process of a solution that enables it to transmit current. According to WHO standards, EC value should not exceeded 400 μS/cm. The current investigation indicated that EC value was 179.3–20 μS/cm with an average value of 192.14 μS/cm. Similar value was reported by Soylak et al. ( 2001 ) drinking water of turkey. These results clearly indicate that water in the study area was not considerably ionized and has the lower level of ionic concentration activity due to small dissolve solids (Table 1 ).

PH of water

PH is an important parameter in evaluating the acid–base balance of water. It is also the indicator of acidic or alkaline condition of water status. WHO has recommended maximum permissible limit of pH from 6.5 to 8.5. The current investigation ranges were 6.52–6.83 which are in the range of WHO standards. The overall result indicates that the Wondo Genet College water source is within the desirable and suitable range. Basically, the pH is determined by the amount of dissolved carbon dioxide (CO 2 ), which forms carbonic acid in water. Present investigation was similar with reports made by other researchers’ study (Edimeh et al. 2011 ; Aremu et al. 2011 ).

Chloride (Cl)

Chloride is mainly obtained from the dissolution of salts of hydrochloric acid as table salt (NaCl), NaCO 2 and added through industrial waste, sewage, sea water etc. Surface water bodies often have low concentration of chlorides as compare to ground water. It has key importance for metabolism activity in human body and other main physiological processes. High chloride concentration damages metallic pipes and structure, as well as harms growing plants. According to WHO standards, concentration of chloride should not exceed 250 mg/l. In the study areas, the chloride value ranges from 3–4.4 mg/l in Wondo Genet Campus, and the mean value of this drinking water was 3.7 mg/l. Similar value was reported by Soylak et al. ( 2001 ) drinking water of Turkey.

Sulfate mainly is derived from the dissolution of salts of sulfuric acid and abundantly found in almost all water bodies. High concentration of sulfate may be due to oxidation of pyrite and mine drainage etc. Sulfate concentration in natural water ranges from a few to a several 100 mg/liter, but no major negative impact of sulfate on human health is reported. The WHO has established 250 mg/l as the highest desirable limit of sulfate in drinking water. In study area, concentration of sulfate ranges from 0–3 mg/l in Wondo Genet Campus, and the mean value of SO 4 was 0.33 mg/l. The results exhibit that concentration of sulfate in Wondo Genet campus was lower than the standard limit and it may not be harmful for human health.

Magnesium (Mg)

Magnesium is the 8th most abundant element on earth crust and natural constituent of water. It is an essential for proper functioning of living organisms and found in minerals like dolomite, magnetite etc. Human body contains about 25 g of magnesium (60 % in bones and 40 % in muscles and tissues). According to WHO standards, the permissible range of magnesium in water should be 50 mg/l. In the study areas magnesium was ranges from 10.42 to 17.05 mg/l in Wondo Genet Campus and the mean value of magnesium in water is 13.67 mg/l. Similar value was reported by Soylak et al. ( 2001 ) drinking water of Turkey. The results exhibit that concentration of magnesium in Wondo Genet College was lower than the standard limit of WHO.

Calcium (Ca)

Calcium is 5th most abundant element on the earth crust and is very important for human cell physiology and bones. About 95 % of calcium in human body stored in bones and teeth. The high deficiency of calcium in humans may caused rickets, poor blood clotting, bones fracture etc. and the exceeding limit of calcium produced cardiovascular diseases. According to WHO ( 2011 ) standards, its permissible range in drinking water is 75 mg/l. In the study areas, results show that the concentration of calcium ranges from 2.16 to 7.31 mg/l in Wondo Genet campus with an average value of 5.08 mg/l.

Sodium (Na)

Sodium is a silver white metallic element and found in less quantity in water. Proper quantity of sodium in human body prevents many fatal diseases like kidney damages, hypertension, headache etc. In most of the countries, majority of water supply bears less than 20 mg/l, while in some countries the sodium quantity in water exceeded from 250 mg/l (WHO 1984 ). According to WHO standards, concentration of sodium in drinking water is 200 mg/1. In the study areas, the finding shows that sodium concentration ranges from 28.54 to 34.19 mg/1 at Wondo Genet campus with an average value of 31.23.

Potassium (k)

Potassium is silver white alkali which is highly reactive with water. Potassium is necessary for living organism functioning hence found in all human and animal tissues particularly in plants cells. The total potassium amount in human body lies between 110 and 140 g. It is vital for human body functions like heart protection, regulation of blood pressure, protein dissolution, muscle contraction, nerve stimulus etc. Potassium is deficient in rare but may led to depression, muscle weakness, heart rhythm disorder etc. According to WHO standards the permissible limit of potassium is 12 mg/1. Results show that the concentration of potassium in study areas ranges from 20.83 to 27.51 mg/1. Wondo Genet College with an average value of 23.14 mg/1. Present investigation was similar with reports made by other researchers’ study (Edimeh et al. 2011 ; Aremu et al. 2011 ). These results did not meet the WHO standards and may become diseases associated from potassium extreme surpassed.

Nitrate (NO 3 )

Nitrate one of the most important diseases causing parameters of water quality particularly blue baby syndrome in infants. The sources of nitrate are nitrogen cycle, industrial waste, nitrogenous fertilizers etc. The WHO allows maximum permissible limit of nitrate 5 mg/l in drinking water. In study areas, results more clear that the concentration of nitrate ranges from 1.42 to 4.97 mg/l in Wondo Genet campus with an average value of 2.67 mg/l. These results indicate that the quantity of nitrate in the study site is acceptable in Wondo Genet campus (Table 2 ).

Bacterial contamination

The total coliform group has been selected as the primary indicator bacteria for the presence of disease causing organisms in drinking water. It is a primary indicator of suitability of water for consumption. If large numbers of coliforms are found in water, there is a high probability that other pathogenic bacteria or organisms exist. The WHO and Ethiopian drinking water guidelines require the absence of total coliform in public drinking water supplies.

In this study, all sampling sites were not detected of faecal coliform bacteria. Figure  1 shows the mean values of total coliform bacteria in drinking water collected from the study area. All drinking water samples collected from Wondo Genet Campus were analyzed for total coliform bacteria and ranged from 1 to 4/100 ml with an average value of 0.78 colony/100 ml. In Wondo Genet College, the starting point of drinking water sources (Dam1), the second (Dam2) and Dam3 samples showed the presence of total coliform bacteria (Fig.  1 ). According to WHO ( 2011 ) risk associated in Wondo Genet campus drinking water is low risk (1–10 count/100 ml).

The mean values of total coliform bacteria in drinking water

According to the study all water sampling sites in Wondo Genet campus were meet world health organization standards and Ethiopia drinking water guideline. Figure  2 indicated that mean value of the study sites were under the limit of WHO standards.

Comparison of water quality parameters of drinking water of Wondo Genet campus with WHO and Ethiopia standards

Effect of water quality for residence health’s

Diseases related to contamination of drinking-water constitute a major burden on human health. Interventions to improve the quality of drinking-water provide significant benefits to health. Water is essential to sustain life, and a satisfactory (adequate, safe and accessible) supply must be available to all (Ayenew 2004 ).

Improving access to safe drinking-water can result in tangible benefits to health. Every effort should be made to achieve a drinking-water quality as safe as practicable. The great majority of evident water-related health problems are the result of microbial (bacteriological, viral, protozoan or other biological) contamination (Ayenew 2004 ).

Excessive amount of physical, chemical and biological parameters accumulated in drinking water sources, leads to affect human health. As discussed in the result, all Wondo Genet drinking water sources are under limit of WHO and Ethiopian guideline standards. Therefore, the present study was found the drinking water safe and no residence health impacts.

On the basis of findings, it was concluded that drinking water of the study areas was that all physico–chemical parameters in all the College drinking water sampling sites, and they were consistent with World Health Organization standard for drinking water (WHO). The samples were analyzed for intended water quality parameters following internationally recognized and well established analytical techniques.

It is evident that all the values of sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), chloride (Cl), SO 4 , and NO 3 fall under the permissible limit and there were no toxicity problem. Water samples showed no extreme variations in the concentrations of cations and anions. In addition, bacteriological determination of water from College drinking water sources was carried out to be sure if the water was safe for drinking and other domestic application. The study revealed that all the College water sampling sites were not contained fecal coliforms except the three water sampling sites had total coliforms.

The study was conducted in Wondo Genet College of Forestry and Natural Resources campus, which is located in north eastern direction from the town of Hawassa and about 263 km south of Addis Ababa (Fig.  3 ). It lies between 38°37′ and 38°42′ East longitude and 7°02′ and 7°07′ north latitude. Landscape of the study area varies with an altitude ranging between 1600 and 2580 meters above sea level. Landscape of the study area varies with an altitude ranging between 1600 and 2580 meters above sea level.

Map of study area

The study area is categorized under Dega (cold) agro-ecological zone at the upper part and Woina Dega (temperate) agro-ecological zone at the lower part of the area. The rainfall distribution of the study area is bi-modal, where short rain falls during spring and the major rain comes in summer and stays for the first two months of the autumn season. The annual temperature and rainfall range from 17 to 19 °C and from 700 to 1400 mm, respectively (Wondo Genet office of Agriculture 2011).

Methodology

Water samples were taken at ten locations of Wondo Genet campus drinking water sources. Three water samples were taken at each water caching locations. Ten (10) water samples were collected from different locations of the Wondo Genet campus. Sampling sites for water were selected purposely which represents the entire water bodies.

Instead of this study small dam indicates the starting point of Wondo Genet campus drinking water sources rather than large dams constructed for other purpose. Taps were operated or run for at least 5 min prior to sampling to ensure collection of a representative sample (temperature and electrical conductivity were monitored to verify this). Each sample’s physico–chemical properties of water were measured in the field using portable meters (electrical conductivity, pH and temperature) at the time of sampling. Water samples were placed in clean containers provided by the analytical laboratory (glass and acid-washed polyethylene for heavy metals) and immediately placed on ice. Nitric acid was used to preserve samples for metals analysis.

Analysis of water samples

Determination of ph.

The pH of the water samples was determined using the Hanna microprocessor pH meter. It was standardized with a buffer solution of pH range between 4 and 9.

Measurement of temperature

This was carried out at the site of sample collection using a mobile thermometer. This was done by dipping the thermometer into the sample and recording the stable reading.

Determination of conductivity

This was done using a Jenway conductivity meter. The probe was dipped into the container of the samples until a stable reading will be obtained and recorded.

Determination of total dissolved solids (TDS)

This was measured using Gravimetric Method: A portion of water was filtered out and 10 ml of the filtrate measured into a pre-weighed evaporating dish. Filtrate water samples were dried in an oven at a temperature of 103 to 105 °C for \(2\frac{1}{2}\)  h. The dish was transferred into a desiccators and allowed cool to room temperature and were weighed.

In this formula, A stands for the weight of the evaporating dish + filtrate, and B stands for the weight of the evaporating dish on its own Mahmud et al. ( 2014 ).

Chemical analysis

Chloride concentration was determined using titrimetric methods. The chloride content was determined by argentometric method. The samples were titrated with standard silver nitrate using potassium chromate indicator. Calcium ions concentrations were determined using EDTA titrimetric method. Sulphate ions concentration was determined using colorimetric method.

Microorganism analysis

In the membrane filtration method, a 100 ml water sample was vacuumed through a filter using a small hand pump. After filtration, the bacteria remain on the filter paper was placed in a Petri dish with a nutrient solution (also known as culture media, broth or agar). The Petri dishes were placed in an incubator at a specific temperature and time which can vary according the type of indicator bacteria and culture media (e.g. total coliforms were incubated at 35 °C and fecal coliforms were incubated at 44.5 °C with some types of culture media). After incubation, the bacteria colonies were seen with the naked eye or using a magnifying glass. The size and color of the colonies depends on the type of bacteria and culture media were used.

Statically analysis

All data generated was analyzed statistically by calculating the mean and compare the mean value with the acceptable standards. Data collected was statistically analyzed using Statistical Package for Social Sciences (SPSS 20).

Abbreviations

ethylene dinitrilo tetra acetic acid

Minstor of Health

nephelometric turbidity units

total dissolved solid

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Authors’ contributions

YM: participated in designing the research idea, field data collection, data analysis, interpretation and report writing; BA: participated in field data collection, interpretation and report writing. Both authors read and approved the final manuscript.

Authors’ information

Yirdaw Meride: Lecturer at Hawassa University, Wondo Genet College of Forestry and Natural Resources. He teaches and undertakes research on solid waste, carbon sequestration and water quality. He has published three articles mainly in international journals. Bamlaku Ayenew: Lecturer at Hawassa University, Wondo Genet College of Forestry and Natural Resources. He teaches and undertakes research on Natural Resource Economics. He has published three article with previous author and other colleagues.

Acknowledgements

Hawassa University, Wondo Genet College of Forestry and Natural Resources provided financial support for field data collection and water laboratory analysis. The authors thank anonymous reviewers for constructive comments.

Competing interests

The authors declare that they have no competing interests.

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Meride, Y., Ayenew, B. Drinking water quality assessment and its effects on residents health in Wondo genet campus, Ethiopia. Environ Syst Res 5 , 1 (2016). https://doi.org/10.1186/s40068-016-0053-6

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Received : 01 September 2015

Accepted : 06 January 2016

Published : 21 January 2016

DOI : https://doi.org/10.1186/s40068-016-0053-6

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