|Year : 2008 | Volume
| Issue : 1 | Page : 6-11
The effect of water purification systems on fluoride content of drinking water
AR Prabhakar, OS Raju, AJ Kurthukoti, TD Vishwas
Department of Pedodontics and Preventive Dentistry, Bapuji Dental College and Hospital, Davangere - 577 004, India
A R Prabhakar
Department of Pedodontics and Preventive Dentistry, Bapuji Dental College and Hospital, Davangere - 577 004
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Objective: The purpose of the present study was to determine the effect of different water purification systems on the fluoride content of drinking water and to compare the efficacy of these water purification systems in reducing the fluoride content.
Materials and Methods: Five different water purification systems were tested in this study. They were reverse osmosis, distillation, activated carbon, Reviva® , and candle filter. The water samples in the study were of two types, viz, borewell water and tap water, these being commonly used by the people of Davangere City, Karnataka. The samples were collected before and after purification, and fluoride analysis was done using fluoride ion-specific electrode.
Results: The results showed that the systems based on reverse osmosis, viz, reverse osmosis system and Reviva® showed maximum reduction in fluoride levels, the former proving to be more effective than the latter; followed by distillation and the activated carbon system, with the least reduction being brought about by candle filter. The amount of fluoride removed by the purification system varied between the system and from one source of water to the other.
Interpretation and Conclusion: Considering the beneficial effects of fluoride on caries prevention; when drinking water is subjected to water purification systems that reduce fluoride significantly below the optimal level, fluoride supplementation may be necessary. The efficacy of systems based on reverse osmosis in reducing the fluoride content of water indicates their potential for use as defluoridation devices.
Keywords: Activated carbon, borewell water, candle filter, defluoridation, distillation, fluoride, ion-specific electrode, reverse osmosis system, tap water
|How to cite this article:|
Prabhakar A R, Raju O S, Kurthukoti A J, Vishwas T D. The effect of water purification systems on fluoride content of drinking water. J Indian Soc Pedod Prev Dent 2008;26:6-11
|How to cite this URL:|
Prabhakar A R, Raju O S, Kurthukoti A J, Vishwas T D. The effect of water purification systems on fluoride content of drinking water. J Indian Soc Pedod Prev Dent [serial online] 2008 [cited 2018 Oct 16];26:6-11. Available from: http://www.jisppd.com/text.asp?2008/26/1/6/40314
| Introduction|| |
It may seem anachronistic to talk about India becoming a superpower in the years to come, when women in our villages have to walk miles to fetch a pot of drinking water. However, the situation is very different in the urban India, where public water supply systems ensure a regular supply of safe drinking water.
Over the last few years, the urban society has taken much greater interest in the quality of drinking water supplied. This has stimulated the use of domestic purification systems to reduce the organic and inorganic contaminants in water.  There are several basic types of water purification systems, e.g., reverse osmosis, distillation, filtration, oxidation, disinfection, cation exchange softening, anion exchange, activated carbon, etc. These systems can be used alone or in combination. ,
Fluoride, the pivot of preventive dentistry, continues to be the cornerstone of caries prevention programmes. Fluoride intake depends on the fluoride content of drinking water, the amount of water ingested, and the fluoride content in other beverages and foods. The recommended level of water fluoridation for optimal dental caries reduction is 0.7 ppm to 1.0 ppm, with 4.0 ppm being the maximum contaminant level allowed by the Environmental Protection Agency. Fluoridation of public water supplies represents one of the most successful public health measures ever undertaken. 
However, there is a growing concern that removal of fluoride by domestic water purification systems may reduce its concentration below the optimum level. If this is so, there will be a temptation to prescribe fluoride supplements even in optimally fluoridated areas. ,,, At the same time, the efficacy of water purification systems in removing fluoride also needs to be evaluated. Therefore, the purpose of the present study was to determine and to compare the effects of different water purification systems on the fluoride content of drinking water.
| Materials and Methods|| |
Water samples used for the study were obtained from two sources, namely, borewells (underground water) and municipal taps (surface water), which are the major sources of drinking water for the people of Davangere City, Karnataka. To avoid the possible reaction of fluoride with glass, water samples were collected and stored throughout the experiment period in plastic containers (polyethylene cans) that had been previously rinsed twice with deionized water to remove any fluoride residue. The samples of water were divided into two groups, the control group and the experimental group.
Control group (unprocessed water): One sample, containing 100 ml of water, was collected from each water source for eight consecutive days for fluoride analysis. This group was considered as the unprocessed water or control group.
Experimental group (processed water): Water from each source was subjected to five different water purification systems, viz, reverse osmosis system, distillation, activated carbon, Reviva® , and candle filter for eight consecutive days prior to fluoride analysis. After purification, 100 ml of water of each source, from each of the five water purification systems, were collected. The samples were stored in coded plastic containers for fluoride analysis. These samples constituted the processed water or the experimental group.
Fluoride analysis was conducted randomly, using an Orion fluoride ion-specific electrode (model: 94-09, 720 A) as per the manufacturer's instructions; it was standardized using 0.1 ppm, 0.2 ppm up to 10 ppm fluoride solutions. Direct measurement was used for estimation, as the sample size was large. For fluoride analysis, equal amounts (20 ml) of each water sample and TISAB (total ionic strength adjustment buffer) solution were combined in a plastic beaker and agitated to remove air bubbles. For each sample, before taking readings, the electrode was rinsed, blot dried, and then placed into the test solution. The solution was stirred thoroughly with the electrode and the steady readings on the meter were noted. The instrument was calibrated every half an hour. The fluoride concentrations in all the 96 samples were recorded and the values were subjected to statistical analysis.
Description of the various water purification systems: ,,,
Reverse osmosis [Figure - 1]: The reverse osmosis system is a drinking water purification system for home use that uses the principle of reverse osmosis to remove molecule-by-molecule all the minerals, chemicals, solid particles, and dissolved contaminants from water. The reverse osmosis system employs a semipermeable membrane that consists of several thin layers or sheets of film that are bonded together and rolled in a spiral configuration around a plastic tube. When the fed water stream passes across the surface of the membrane, the molecules penetrate the membrane surface, working their way around the spiral and collecting in the center tube. The remaining contaminants are concentrated on the surface of the membrane and can be washed away.
Distillation [Figure - 2]: It is a process that removes water from the contaminant. It heats up the water to boiling point, traps the rising steam, and uses a fan or cooling device to condense the vapor back into the original form. Water distillation is the most effective method for the removal of organic, inorganic, and biological (bacteria, viruses, etc.) contaminants.
Activated carbon [Figure - 3]: This system employs an absorbent material, usually solid, which is capable of adsorbing gases, liquids, and suspended matter on to its surface.
Reviva® (Eureka Forbes) [Figure - 4]: This is a commercially available water purification system. It contains filtering components: (1) a pre-sediment filter which removes undissolved particles from the water. It protects the membrane and pre-carbon filter from clogging; (2) Pre-silver carbon filter which removes chlorine, pigments, detergents, carcinogens, heavy metals, and other impurities; (3) a semipermeable membrane which removes most of the dissolved substances; and (4) a post-silver carbon filter which removes odor and improves water taste. Non-filtering components include a booster pump and a pressure reducer valve Reviva.
Candle filters: They are household filters having an upper housing chamber fitted with the candles. The water percolated throught the candle and collected in the lower storage chamber [Figure - 5].
| Results|| |
The mean, standard deviation, and percentages were determined for each of the test groups. The paired t -test was used to determine the difference between paired observations. The unpaired t -test was used for comparison of fluoride reduction by different water purification systems. Significance for all the statistical tests was predetermined at a P -value of 0.05 or less.
Observations [Table - 1]: Unprocessed borewell and tap water samples showed mean fluoride values of 3.51 ± 0.02 and 0.26 ± 0.02, respectively [Table - 1]. In the borewell group, processed water samples showed a reduction of about 72.2% in the fluoride content by reverse osmosis system, 55.6% by distillation, 28.9% by activated carbon, 63.9% by Reviva® , and only 2.4% by candle filter; these differences were statistically highly significant ( P < 0.001). Processed tap water samples showed a reduction in the fluoride content of about 37.9% by reverse osmosis system, 17.5% by distillation, 14.6% by activated carbon, and 21.4% by Reviva® , which was statistically highly significant ( P < 0.001); by candle filter the reduction was only 1.5%, which was statistically significant ( P < 0.05).
[Table - 2] shows the difference in fluoride reduction between all the water purification systems used. The fluoride reduction in borewell and tap water by reverse osmosis system when compared with other purification systems was statistically highly significant ( P < 0.001). The fluoride reduction in borewell water by distillation system when compared with activated carbon, Reviva® , and candle filter was statistically highly significant ( P < 0.001). In tap water, the fluoride reduction by distillation, compared to activated carbon and Reviva® , was statistically not significant ( P > 0.05) but was highly significant compared to candle filter ( P < 0.001). Activated carbon system, when compared with Reviva® and candle filter, showed statistically highly significant ( P < 0.001) fluoride reduction in borewell water. In tap water, however, the fluoride reduction with the activated carbon system was not statistically significant when compared to Reviva® ( P > 0.05) but was significant when compared to that of candle filter ( P < 0.05). The fluoride reduction by Reviva® when compared to that by candle filter in both the groups, was statistically highly significant ( P < 0.001).
| Discussion|| |
The use of water purification systems has increased dramatically since its inception many years ago and is gaining popularity as people are becoming increasingly concerned about the pollutants present in public water supplies. The purpose of using these systems is to remove or modify impurities in the water. Most domestic users seek to improve the taste and quality of their drinking water by using a relatively simple filter to remove unwanted impurities such as inorganic salts, heavy metals, and suspended and colloidal matter.  Some manufacturers claim to remove specific elements such as chlorine and, therein, the possibility exists that the fluoride content would be affected. 
Excessive consumption of fluoride above the optimal level causes dental and skeletal fluorosis. But, in drinking water, to prevent caries, the fluoride content needs to be reduced to the optimal level. The importance of the fluoride ion in cariostasis is well documented. In some studies, fluoride supplementation did not affect the likelihood of developing caries, which may have been due to low compliance or over-reporting of their use. , Studies have shown that the consumption of unfluoridated bottled and tank water may put children at increased risk of developing caries. , Caries experience in deciduous teeth was highest for children with the greatest lifetime consumption of such water. 
Any interference with this important ion is of interest to dentists as knowledge of the fluoride intake is important for determining the dosage of fluoride supplements or the necessity of topical fluorides in the patients. The present study investigated the extent to which water purification systems remove fluoride from drinking water. Determination of the most appropriate levels of fluoride in drinking water is crucial for both types of communities: the ones that intend to start water fluoridation as well as for those that have excessive natural fluoride in their drinking water and therefore require defluoridation. The purification systems selected for the study were available either separately or as a combination of systems for household use. In some earlier studies, either fluoridated water or laboratory water samples were used; , in other studies water from natural sources were taken as samples. , Ion-specific electrode was selected for fluoride analysis because it has been found to be accurate to within 0.5%, i.e., it is about 98% accurate. ,
Fluoride analysis of the control group samples showed that the mean fluoride levels in tap water were very low: 0.26 ± 0.02, whereas that of borewell water was high: 3.51 ± 0.02, being above the recommended limit of 1 ppm. However, it should be noted that groundwater fluoride levels vary from one source to another. The results from the present study revealed that the reverse osmosis system removed substantial amounts of fluoride from borewell and tap water, i.e., 72.2% and 37.9%, respectively. It also revealed that fluoride reduction by the reverse osmosis system, compared to other systems in both the groups, was maximal and was statistically highly significant. The results are in accordance with the previous studies by Jobson et al. ,  Glass,  and Brown and Aaron.  Variations in the degree of reduction may be due to differing pressure levels and clogging of the membranes. 
The distillation system caused highly significant reduction in fluoride levels in both the groups, i.e., 55.6% in borewell and 17.5% in tap water. The fluoride reduction by the distillation system was greater than that by activated carbon and candle filter and lesser than that by reverse osmosis and Reviva® in both the groups. The results were statistically highly significant in both the groups, except for the activated carbon and Reviva® systems in the tap water group, where it was not statistically significant. The distillation system achieved the third best fluoride reduction in both the groups. Previous studies by Jobson et al .  and Brown and Aaron  have reported more than 95% fluoride reduction.
In this study, a fluoride reduction of 28.9% in borewell water and 14.6% in tap water groups by the activated carbon system was observed. Fluoride reduction by activated carbon was greater than that by candle filter and lesser than that by reverse osmosis, distillation, and Reviva® in both the groups. The results were statistically highly significant in both the groups, except with Reviva® in the tap water group, where it was not statistically significant. Previous tests based on activated carbon have given contradictory results.  While Jobson et al. ,  Glass,  and Brown and Aaron  have reported fluoride reduction, Robinson et al.  and Buzalaf et al.  have reported that very few activated carbon filters remove fluoride. This could be attributed to the variations between different manufacturers and designs.  In our study, fine granules of activated carbon were used and this must have resulted in exposure of greater surface area for fluoride adsorption.
The Reviva® water purification system, containing a reverse osmosis membrane and pre- and post-silver carbon filters, showed highly significant fluoride reduction in both the groups, i.e., 63.9% in borewell and 21.4% in tap water. The fluoride reduction by Reviva® , compared to that by candle filter, was very high in both the groups and was statistically highly significant. These values indicate that the Reviva® purification system was the second best in fluoride removal. Fluoride reduction by candle filter was 2.4% in the borewell group, whereas there was only 1.5% reduction in the tap water group. The fluoride reduction by candle filter was minimal. From the observations made so far, we found that the systems based on reverse osmosis, viz, reverse osmosis system and Reviva® brought about the maximum reduction in water fluoride levels. The variations in fluoride reductions by these systems may be attributed to differences in the type of membrane and differing pressure lines; regular maintenance of equipment may also influence its efficacy in fluoride reduction. 
Water purification systems such as reverse osmosis system, Reviva® , distillation, and activated carbon filter can effectively reduce the amount of fluoride content in drinking water. The results indicate that the amount of fluoride removed due to purification varies from one type of system to the other and from one source to the other. Part of the variation in results may be accounted for by the method of investigation. 
According to American Dental Association (ADA) and AAPD (American Academy of Pediatric Dentistry) guidelines, children receiving water fluoridated at less than 0.7 ppm should receive fluoride supplements. , Accurate prescription of fluoride is possible only when the water fluoride concentration is known. One should also take into account the carry-over or diffusion effect of fluoride. 
As the general population becomes increasingly concerned about polluted drinking water, domestic water purification systems are becoming very popular.  In homes, when employing a domestic purification system, the fluoride levels of drinking water need to be monitored, as the children in these houses may need fluoride supplementation. It is also our recommendation that water purification systems employing monitored reverse osmosis process be used in the fluorosis endemic areas, as this mode of filtration is known to most efficiently filter fluoride. The possibility of using domestic water purification systems as defluoridating units needs to be further explored.
| Conclusion|| |
- The amount of fluoride removed due to purification varies from one type of system to the other and from one source to the other.
- Systems based on reverse osmosis, viz, reverse osmosis system and Reviva® , showed maximum reduction in fluoride levels, the former showing greater reduction; these two systems were followed in efficiency by distillation and the activated carbon system, with the least reduction being brought about by the candle filter.
Considering the beneficial effects of fluoride on caries prevention, drinking water subjected to water purification systems that reduce fluoride significantly below the optimal level may require fluoride supplementation. Efficient fluoride reduction by systems based on reverse osmosis encourages their use as defluoridation devices, provided there is stringent supervision. We recommend the use of monitored reverse osmosis systems in the fluorosis endemic areas.
Based on the results of this study, more rigorous surveillance and monitoring of water fluoride levels are recommended. Evaluation of filtration systems, using different water sources from different geographical locations, should provide useful information.
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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5]
[Table - 1], [Table - 2]
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