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 Table of Contents  
Year : 2020  |  Volume : 5  |  Issue : 3  |  Page : 72-77

Chemical analysis of drinking water to compare reverse osmosis processed and unprocessed water quality

Department Community Medicine, Jhalawar Medical College, Jhalawar, Rajasthan, India

Date of Submission03-Jun-2020
Date of Decision04-Aug-2020
Date of Acceptance30-Aug-2020
Date of Web Publication30-Sep-2020

Correspondence Address:
Dr. Shakila Mulla
In Front of SRG Hospital, Near Ronak Medical Store, Kota Road, Jhalawar - 326 001, Rajasthan
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ed.ed_21_20

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Context: Reverse osmosis (RO) is a water purification technology that uses semi-permeable membrane to remove ions, molecules, and larger particles from drinking water. However, it is to be remembered that water contains range of minerals, necessary for the human body. Low mineral content has been observed to cause various health hazards such as dental caries, hypertension, and coronary artery disease.
Aims: The aim of this study is to perform the chemical analysis of drinking water processed by RO in terms of total dissolved solids (TDS), hardness and fluoride and to compare it with RO-unprocessed (non-RO) water and further to find the association with health hazards such as dental caries and cardiovascular diseases (CVD).
Materials and Methods: A community-based observational study was conducted on medical and para-medical staff families. For qualitative data, the Pearson's Chi-square test and for quantitative data, Student's t and ANOVA tests were applied. Pearson correlation coefficient was calculated to know the correlation between TDS and hardness of water and represented in a Scatter Diagram.
Results: Out of 466 families, 231 were RO users and 235 were non-RO users. Even after practicing regular servicing of RO unit by the majority RO-users, mean values of TDS, hardness and fluoride were significantly less than RO unprocessed water and were also less than the desired minimum values. Positive family history of dental caries and CVD was significantly associated with the use of RO water.
Conclusion: RO process diminishes the chemical quality of drinking water in terms of TDS, hardness, and fluoride and is associated with health hazards. Standardization of chemical quality of RO purifiers for domestic use is equally important as it is being carried out commercially.

Keywords: Dental caries, fluoride in drinking water, reverse osmosis, total dissolved solids, water hardness

How to cite this article:
Singh D, Mulla S. Chemical analysis of drinking water to compare reverse osmosis processed and unprocessed water quality. Environ Dis 2020;5:72-7

How to cite this URL:
Singh D, Mulla S. Chemical analysis of drinking water to compare reverse osmosis processed and unprocessed water quality. Environ Dis [serial online] 2020 [cited 2023 Jun 3];5:72-7. Available from: http://www.environmentmed.org/text.asp?2020/5/3/72/296804

  Introduction Top

Requirement of water for the very existence of life has driven human to devise methods for its purification.[1] Water supplies are highly variable in their mineral contents. Consumption of moderate hard water (60–120 mg/L) is associated with somewhat lowered risk of cardio-vascular diseases (CVD).[2],[3] It has been suggested that certain types of cardiac disease may be aggravated by the lack of calcium, because it is required for muscle contractions and has been shown to decrease serum lipid levels.[2],[3] Later, a more complex mechanism was suggested, involving the ratio of magnesium and calcium to sodium.[4] Increased mortality in “soft water” areas is linked to increased frequency of hypertension.[5] A study found that the mean myocardial magnesium of those who died from Ischemic Heart Disease was 22% lower than the age-adjusted mean of those who died accidentally.[6]

Drinking water is the important source of fluoride. Fluoride is most effective in dental caries prevention when a low level of fluoride is constantly maintained in the oral cavity.[7] The optimal drinking water concentration of fluoride for dental health is generally between 0.5 and 1 mg/L.[8] Dental caries is the most prevalent oral disease in the several countries of Asia and Latin America.[7] The reason for this appears to be increasing consumption of sugar and inadequate exposure to fluoride.[9]

The use of low-mineral water for cooking food may cause a marked deficiency in some essential elements.[10] The WHO 1980 report recommended that the minimum total dissolved solid (TDS) in drinking water should be 100 mg/L.[11]

The popularity of reverse osmosis (RO) water has been steadily increasing since it was first introduced as a home water purification system in the 1970s.[12] RO system membrane provides a form of “hyper-filtration” by restricting the passage of many substances.[8] Membrane processes can remove a broad spectrum of minerals.[13]

Unfortunately, over the past two decades, little research attention has been given to the beneficial or protective effects of drinking water substances.[10] In the current study, objectives were to estimate and compare the levels of TDS, hardness, and fluoride in RO processed and unprocessed drinking water and additionally to find out and compare the prevalence of dental caries and CVD among families. In addition, knowledge and perception about the chemical quality of drinking water and utility of RO were also assessed.

  Materials and Methods Top

The current study is a community-based observational study. To perform the chemical analysis of drinking water samples, both RO processed and unprocessed water samples were collected from the community after obtaining written informed consent of each study participant. The study population comprised of medical and paramedical staff of the parent medical college. The parent medical college has 171 medical staff and 389 paramedical staff, making a total of 560. The current study sample was taken as complete enumeration. During the collection of data, it was found that there are many couples working in the medical college. A total of 92 couples were found among 560 staff. As the drinking water source was same for a couple, instead of two, single water sample was collected for the current study. Two staff members were out of station throughout the period of study, so they were excluded. This led to the final sample size of 466.

The duration of the study was 2 months, August and September 2018. Ethical approval was obtained from the Institutional Ethical Committee before commencing the data collection. Water samples were collected from the study participants after obtaining written informed consent.

Whole study sample families reside in the urban area where water supply is from the municipal corporation. Considering the irregularity of water supply, many families rely on tube wells (underground water) as a main water supply source. The use of RO process for drinking water is common in the community. By including both medical and paramedical staff, it was desired to obtain RO processed and unprocessed water samples for the comparison.

For data collection, each staff member's family was visited. A predesigned pro forma containing the details of water purification, history of dental caries and/or CVD in the family, awareness about chemical quality of drinking water and perception about utility of RO purifier, was filled up by the interviewer at the time of family visit. In addition, a sample of water was collected from each family in the clean container and labeled.

Three competent tests were conducted to establish the chemical composition of water, i.e., level of TDS, hardness, and fluoride in mg/L. The principal constituents of TDS are usually calcium, magnesium, sodium, and potassium cations and carbonate, chloride, sulfate, and nitrate anions.[14] TDSs level between 100 and 300 mg/L are considered normal for the current study. Hardness of water is caused by dissolved polyvalent metallic ions, predominantly calcium and magnesium cations, although other cations (e.g., aluminum, barium, iron, manganese, strontium, and zinc) also contribute.[15] Acceptable hardness for drinking water is moderately hard (60–120 mg/L). As fluoride between 0.5 and 1 mg/L reduces the incidence of dental caries,[16] this level was considered normal in the current study. For TDS estimation, digital generic TDS meter, model number CPEX10001 was used. For the estimation of hardness and fluoride levels, Aquasol Total Hardness Test Kit A201 and Aquasol Fluoride Test Kit AE210 were used, respectively. The kits are manufactured by the International Organization for Standardization (ISO) certified company “Rakiro” (ISO 9001:2015) which is also certified by Haffkine Institute for Training, Research, and Testing, Mumbai. Both the kits require the series of chemical tests by the titrimetric method.

For the statistical analysis, SPSS software version 20 (IBM, Bengaluru, Karnataka. India) was used. For qualitative data, percentages were calculated, and Pearson's Chi-square test was applied to test the relationship of adverse health status with the method of water purification. For quantitative data, Student's t-test was applied to find out any significant difference in the results of chemical tests for RO processed and unprocessed water. The ANOVA test was applied to test the differences among the mean values of chemical tests on water samples based on the sources of water supply. Pearson correlation coefficient (r) was calculated to know the correlation between TDS and hardness of water. It is also represented graphically in a Scatter Diagram.

  Results Top

Out of 466 water samples, 231 were RO and 235 were non-RO. For majority samples (54.3%), source of water was underground. The Municipal Corporation supply was found for 195 (41.8%) staff members and 18 (3.9%) staff members were using camper water (commercial water supply) as source of water. Frequency distribution for different characteristics of RO and non-RO water using staff members is shown in [Table 1].
Table 1: Frequency distribution of different variables among reverse osmosis and nonreverse osmosis samples

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Twenty (8.66%) staff members do not know about the regular servicing practices of RO unit. This included 18 members using water campers who were not aware of the practices undertaken by the suppliers. Two of the members had started using RO for <3 months duration, so servicing practices were not applicable to them. There were 12 staff members who gave no specific reason for opting RO water purifier. Most of them started using RO as a part of common practices or trend being followed in the neighborhood. Among non-RO users, 17 (7.23%) members do not use any of the drinking water purification method not even straining.

While assessing the perception of non-RO users about RO, 16 members critically answered it as RO is needed only if required. They consider RO process should only be used if the drinking water source has high hardness like in case of underground water. About half of the non-RO users do not know utility of RO water.

TDS of entire 466 samples showed wide range of 8–780 mg/L. Similarly, hardness of water in study samples ranged from 5–750 mg/L and fluoride 0.1–7 mg/L. Values of TDS, hardness and fluoride are compared with the use of RO and non-RO water, as shown in [Table 2].
Table 2: Chemical quality analysis of reverse osmosis and nonreverse osmosis water samples

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Mean TDS, hardness, and fluoride values were found for different water sources. Difference among the group means was analyzed by the ANOVA test. Mean values for underground water were very high as compared to the municipal supply water and camper water. This difference was found statistically very highly significant (P < 0.0001 for each of three analyses) with F = 45.59, 40.38, and 14.76, respectively, for TDS, hardness, and fluoride.

All camper water samples belonged to RO water. Based on the source of water, the use of RO or non-RO method was comparable. In municipal supply water samples, the use of RO was found 46.7% and non-RO 53.3%. In underground source of water, the use of RO was 48.2% and non-RO 51.8%.

The correlation between TDS and hardness was calculated for entire water samples in the current study, and it was found significantly correlated (Pearson correlation r = 0.97, P < 0.0001) with each other, as shown in [Figure 1].
Figure 1: Linear correlation between total dissolved solid and hardness of drinking water

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History of dental caries among the whole study population was obtained from 25.3% families and that of CVDs from 22.7% families. CVDs comprised of ischemic heart disease, hypertension, cerebrovascular disease, congenital heart disease or rheumatic heart disease. The presence of dental caries and CVD in families was analyzed to find out the association with type of drinking water (RO or non-RO) by using the Chi-square test [Table 3].
Table 3: Association between type of drinking water and health hazards

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As health hazards were significantly associated with the use of RO water, the association with years of RO use was further analyzed by finding the difference between mean years of RO use. Mean years of use was significantly more among the study participants having a family history of dental caries (t = 2.405, df = 229 and P = 0.017), but it was not statistically significant for a family history of CVDs (t = 1.81, df = 229 and P = 0.072).

  Discussion Top

The current study sample comprised of medical and para-medical staff of a medical college, who are supposedly more aware about health than the rest of the community. Drinking water quality is one of the vital health determinants. In the current study, out of 466 water samples, nearly half samples were RO processed and remaining half unprocessed (non-RO). Chemical quality of drinking water varies depending on the source of water. More than half staff members use underground water for drinking. Eighteen (3.9%) staff members were using camper water for drinking as they consider underground water very hard for drinking and use it only for other domestic activities.

Out of 231 RO users, 83.98% were regularly servicing their RO unit which is a good practice. Still, 51.52% of RO users do not know about health hazards of low minerals in drinking water. This shows poor knowledge about drinking water chemical quality among health staff. More than half of RO users mentioned a reason for installing RO unit as “to prevent water-borne infections.” This response not only proves concern regarding the microbiological aspect of drinking water but also shows their unawareness regarding the fact that this purpose can be solved using ultra-violet water purifiers instead of RO. Further, 5.19% staff did not need a reason to opt for RO. This is the result of blindly following the practices of mass. Among 235 non-RO users, the most common method of water purification is straining. Overall, knowledge and practices of the study population prove that the chemical aspect of drinking water quality is quite neglected. Only 6.81% of non-RO users possess the correct perception of utility of RO unit.

Mean TDS, hardness and fluoride values are less than desired minimum values (100 mg/L, 60 mg/L and 0.5 mg/L respectively) in the group of RO users. Even though majority of RO users were regularly servicing their RO unit, chemical quality of drinking water was low. Significant difference between mean TDS, hardness and fluoride values of RO and non-RO group indicates that the use of RO is profoundly lowering the chemical quality of drinking water. Similar results were found by the researchers in a study on drinking mineral water.[17] Their results show that the levels of dissolved minerals in the RO drinking water samples were very low, which is quite alarming. Particularly, calcium and magnesium were found in very low amount. The TDS of sample was alarming low, 9.44 mg/L. It may pose negative effects on human health, especially malnourished people's health.[17]

Significantly high mean TDS, hardness, and fluoride values for underground water as compared to municipal supply and camper water is obvious in the current study. Underground water is high in mineral content as compared to municipal supply which commonly uses the surface water like river in the current study.

One additional finding of this study was strong linear correlation between TDS and hardness of water. TDS meter is quite handy to use as compared to the estimation of hardness of water which requires the series of chemical reactions. The estimation of TDS of water alone can predict the hardness status of drinking water.

Hardness of drinking water is an established factor in causation of CVDs. Some studies report that higher the hardness of water lowers the incidence of CVDs.[18],[19],[20] In the current study, very highly significant association was found between the use of RO and history of CVD in families consuming RO water. This finding could be the result of low hardness level in RO water. Similarly, very highly significant association between the use of RO and history of dental caries in the family could be the result of low fluoride level in RO water. Fluoride is one of the most important mineral in the ground water that prevents the tooth decay and controls the metabolic bone diseases.[21] A study on water samples showed a reduction in fluoride content in the range of 0.270–0.457 ppm after passing through various RO filters.[22] Study states that, RO system will worsen the existing condition in areas where water fluoride concentration is suboptimal or low and intake of fluoride from other sources is insufficient.[22] Other studies also concluded that, water purifier devices decrease the fluoride content of water, an issue which should be considered in low fluoridated water sources.[23],[24]

Family history of dental caries was significantly associated with more years of RO use, but family history of CVDs was not statistically associated with mean years of RO use. This might be because of the limitation of the current study that it was not prospective study and presence of CVD was based on a history provided by the participant and was not confirmed by any method. Still, the current study has strongly proved the disadvantages of RO water in terms of lowered chemical quality of drinking water and association with dental caries and CVD. Further, studies are required to establish the association of RO water consumption with the occurrence of various health hazards. In addition, there is a need of community awareness regarding the indiscriminate consumption of RO water without understanding its utility and proper use.

In India, packaged drinking water available for the commercial use has to follow the strict guidelines laid down by the Bureau of Indian Standards.[25] It is a need of time to bring about the standardization of chemical quality for all RO water purifiers by the policy-makers to avoid possible health hazards related with long-term consumption of RO water at the domestic level.

  Conclusion Top

RO lowers the chemical quality of drinking water in terms of TDS, hardness and fluoride. Consumption of RO water is associated with a higher prevalence of dental caries and CVD. To analyze the long-term health hazards of RO use, a prospective study covering larger population needs to be conducted.


The authors would like to thank ICMR, New Delhi, India, for approving this research project under the STS-2018 programme.

The authors are thankful to the entire staff of the department of community medicine of parent medical college for rendering help throughout data collection.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Verma KC, Kushwaha AS. Demineralization of drinking water: Is it prudent? Med J Armed Forces India 2014;70:377-9.  Back to cited text no. 1
Speckmann EW, Brink MF. Relationships between fat and mineral metabolism – A review. J Am Diet Assoc 1967;51:517-22.  Back to cited text no. 2
Bierenbaum ML, Fleischman AI, Raichelson RI. Longterm human studies on the lipid effects of oral calcium. Lipids 1972;7:202-6.  Back to cited text no. 3
Crawford MD. Hardness of drinking-water and cardiovascular disease. Proc Nutr Soc 1972;31:347-53.  Back to cited text no. 4
Crawford MD, Crawford T. Lead content of bones in a soft and a hard water area. Lancet 1969;1:699-701.  Back to cited text no. 5
Anderson TW, Hewitt D. Letter: Mortality and water hardness. Lancet 1975;1:868.  Back to cited text no. 6
Petersen PE. The World Oral Health Report 2003: Continuous improvement of oral health in the 21st century-the approach of the WHO Global Oral Health Programme. Community Dent Oral Epidemiol 2003;31 Suppl 1:3-23.  Back to cited text no. 7
Cotruvo J. Desalination guidelines development for drinking water. In: Background; WHO Library: Nutrients in Drinking Water. Geneva: WHO Press; 2005. p. 8, 9, 13-23.  Back to cited text no. 8
Jones S, Burt BA, Petersen PE, Lennon MA. The effective use of fluorides in public health. Bull World Health Organ 2005;83:670-6.  Back to cited text no. 9
Kozisek F. Health risks from drinking demineralised water. In: National Institute of Public Health, Czech Republic. Nutrients in Drinking Water. Geneva: WHO Press; 2005. p. 150, 151, 158.  Back to cited text no. 10
WHO Report. Guidelines on Health Aspects of Water Desalination. ETS/80.4. Geneva: World Health Organization; 1980.  Back to cited text no. 11
Saini RD. Health risks from long term consumption of reverse osmosis water. Int J Applied Chem 2017;13:293-301.  Back to cited text no. 12
World Health Organization. WHO Guidelines for Drinking Water Quality. 4th ed. Geneva, Switzerland: World Health Organization; 2011. p. 172, 19.  Back to cited text no. 13
World Health Organization. Guidelines for Drinking-Water Quality. Vol. 2., 2nd ed. Total Dissolved Solids in Drinking Water. Geneva: World Health Organization; 1996.  Back to cited text no. 14
Hardness in Drinking-Water. Background Document for Development of WHO Guidelines for Drinking-water Quality. World Health Organization; 2011. p. 1.  Back to cited text no. 15
Adair SM, Bowen WH, Burt BA, Kumar JV, Levy SM, Pendrys DG. Recommendations for using fluoride to prevent and control dental caries in the United States. Morbidity Mortality Weekly Rep CDC 2001;50:1-42.  Back to cited text no. 16
Islam MR, Islam Sarkar MK, Afrin T, Rahman SS, Talukder RI, Howladar BK, et al. A study on total dissolved solids and hardness level of drinking mineral water in Bangladesh. Am J Applied Chem 2016;4:164-69.  Back to cited text no. 17
Heyden S. The hard facts behind the hard-water theory and ischemic heart disease. J Chronic Dis 1976;29:149-57.  Back to cited text no. 18
Hall P, Jungner I. Hard drinking water and ischemic heart disease: Calcium, bloodlipids, and acute myocardial infarcts. J Med Syst 1993;17:277-81.  Back to cited text no. 19
Malpas P, Lloyd S, Lowe CR, Roberts CJ, West RR, Gyntelberg F, et al. Cardiovascular disease in hard and soft water areas. Lancet 1973;301:321.  Back to cited text no. 20
Sumalatha M, Kumanan R, Prabhakar P, Shanti Priya S, Ravi Kumar K, Santhosh B. Hydrology-assessment of quality of water from Nalgonda district. Int J Chem Sci 2012;10:239-56.  Back to cited text no. 21
Khairnar MR, Jain VM, Wadgave U, Dhole RI, Patil SJ, Chopade SR. Effect of different reverse osmosis water filters on fluoride content of drinking water. J Indian Assoc Public Health Dent 2018;16:165-8.  Back to cited text no. 22
  [Full text]  
Jaafari-Ashkavandi Z, Kheirmand M. Effect of home-used water purifier on fluoride concentration of drinking water in Southern Iran. Dent Res J (Isfahan) 2013;10:489-92.  Back to cited text no. 23
Prabhakar AR, Raju OS, Kurthukoti AJ, Vishwas TD. The effect of water purification systems on fluoride content of drinking water. J Indian Soc Pedod Prev Dent 2008;26:6-11.  Back to cited text no. 24
[PUBMED]  [Full text]  
Manual for packaged drinking water. Bureau of Indian Standards (BIS) 2005;1:77-8.  Back to cited text no. 25


  [Figure 1]

  [Table 1], [Table 2], [Table 3]


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