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Fluoride(F-) is the 13thmost abundant chemical element in the Earth's crust which has been widely recognised for its health benefits at low concentration but poses a serious threat to public health at very high doses. The world health organization has set the fluoride guideline limit of 1.5 mg/l in drinking water. Globally, over 260 million people drink water with high fluoride concentrations. Widespread distribution and high fluoride levels in the potablewater in most of the areas of the world has prompted substantial research and mitigation efforts to address the growing public health concerns related to fluoride contamination. With the recent advances in science, various defluoridation methods such as adsorption, ion exchange, precipitation-coagulation, membrane processes, biological defluoridation and even integrated approaches have been developed for the management of fluoride-contaminated aquatic environments. This review provides an up-to-date insight into thedefluoridation techniques developed and implemented throughout the world and highlightsthe advantages and disadvantages of each technique.The literature survey confirms that despite developing so many novel techniques for defluoridation over the years, there is still no effective fluoride removal technique that can achieve the desired results in a cost-effective and sustainable manner. Therefore, development of a commercially practical, economical, and sustainable technique is required to prevent people especially the most vulnerable from poor and developing nations (dependent on untreated water)from the hazards of fluoride contamination.

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Water quality parameters viz. air temperature (15.21 0 C -36 0 C/16.71 0 C - 39.42 0 C), water temperature (13 0 C-32.42 0 C/15 0 C-32.8 0 C), depth (42cm-69.08cm/ 25cm-121.92cm), turbidity (3.88-46.27NTU/3.67-69.39 NTU), salinity (0.10-0.31ppt/ 0.10-0.37ppt), electrical conductivity (0.101-0.172mS/cm/0.114-0.279mS/cm), TDS (49.63-111.78 mg/l/57.64-177.01mg/l), pH (7.92-9.82/7.80-9.09), free CO2 (0-19.22mg/l/0-15.32mg/l), DO (6.82-9.90mg/l/4.65-9.40mg/l), carbonate (0-18.38mg/l/0-20.63mg/l), bicarbonate (60.99-170.70mg/l/77.62-168.70mg/l, chloride (7.41-12.35mg/l/9.59-19.60mg/l), calcium (6.85-38.50mg/l/11.81-140.49mg/l), magnesium (4.62-7.22mg/l/3.86-39.05mg/l), total hardness (40.29-125.50 mg/l/56.61-511.05mg/l), BOD (3.12-5.79mg/l/1.31-16.21 mg/l), COD (17.74-75.42 mg/l/ 26.57-73.03mg/l), sodium (14.2-22.5mg/l/12.2-30.9mg/l), potassium (1.83-4.17mg/l/2.25-6.21mg/l), phosphate (0.048-0.233mg/l/0.008-0.603mg/l), nitrate (0.13-1.3mg/l/0.11-4.08mg/l), sulphate (1.60-19.19mg/l/1.36-15.70mg/l), silicate (0.14-4.23mg/l/0.27-7.05mg/l), iron (0-0.65/0-0.40mg/l), copper (below detectable limit) and zinc (below detectable limit), of lake Surinsar-the only source of drinking water to the inhabitants of the Surinsar village, have been reported monthly, during the year 2002-03/2003-04. WQI range falls from poor (70.45, December; 73.55, October; 74.4, November and 74.56, September/ 74.52, January and 75.36, September), very poor(82.54, February; 89.25, May; 80.76, August and 78.86, January/ 80.89, February; 98.25, April; 80.03, June; 82.26, July; 86.55, October and 83.03, November) to unfit (100.44, June; 101.9, July; 103.86, April and 119.5, March/ 103.73, May; 108.28, March; 122.56, August and 103.72, December). Comparison of range of various water quality parameters of Surinsar lake water, with national and international standards has also revealed that most of these parameters are beyond permissible limits. This clearly indicates the unsuitability of raw water, generally consumed by local inhabitants, for human consumption.

In the present study, an attempt has been made to evaluate the water quality changes in River Tawi water treated at Sitlee water treatment plant, and supplied for drinking to Old Jammu City, Jammu, J&K, India. Water samples from the treated water unit of Sitlee water treatment plant and around ten houses from the distribution point (Old Jammu City) were analyzed monthly for various physicochemical parameters for a period of one year (February 2014 to January 2015. The study indicated deterioration of drinking water quality during its passage through the distribution network which has been attributed to the leakages and defects in the old pipe system supplying water to the Jammu city. Comparison of analyzed water quality parameters with the drinking water standards prescribed by World Health Organization (WHO) and Bureau of Indian Standards (BIS) indicated that parameters like DO (7.49-8.24mg/l), calcium(49.93-67.08mg/l), magnesium (16.14-25.21mg/l) and potassium(6.99-7.93mg/l) were almost nearing the desirable limits but were within the permissible limits and parameters like turbidity(3.5-8.17 NTU) and total hardness(78.87-120.50mg/l) were above the desirable limits in the water samples collected from the distribution point. The collected primary data for the thirteen water quality parameters has been used to calculate the Arithmetic Water Quality Index(WQI) which has shown monsoon increase with higher values at distribution point(65.65). One time microbial analysis (MPN/100ml) for total and faecal coliform has indicated presence of faecal coliform (<1/100ml) in water samples from eight households at distribution point which indicates contamination of water with human faecal matter during its passage through the distribution network. According to microbial standards laid down by Central Pollution Control Board (2008), water contaminated with faecal coliform is unfit for drinking without conventional treatment.