One in 10 sources of drinking water in the State has turned “non-potable” from high concentrations of fluoride, according to an extensive survey of groundwater quality in Karnataka sponsored by the Union Ministry of Drinking Water and Sanitation during 2009–14.

Tests on 41,368 water samples found that 4,039 sources have fluoride well above the permissible limit of 1.5 mg/litre. Fluoride levels were dangerously high in parts of Kolar (7 mg/l) and Tumkur (6.5 mg/l).

When consumed in excessive quantities, the mineral can lead to a debilitating condition called skeletal fluorosis that stiffens bones and joints. Fluoride was particularly extensive in Bellary (489 water sources), Chitradurga (360), Tumkur (689), Chickballapur (689) and Kolar (289 sources).

Fluoride enters aquifers through a natural weathering of granite rocks, and gets increasingly concentrated as the groundwater dips. Groundwater has plummeted to more that 1,000 feet in several parts of the State — particularly in the northern districts and in Bangalore, said M.V. Shahshirekha, a chemist and consultant with the Karnataka Remote Sensing Application Centre, which coordinated the study in the State.

The survey found the high prevalence of another pollutant, nitrate, a compound that enters the groundwater primarily from nitrate-based fertilizer and sewage. As many as 4,156 drinking water sources were contaminated with nitrate in quantities higher than the permissible limit of 45 mg/l.

Bangalore Urban had among the highest levels of the chemical: 399 samples showed high nitrate, and one sample showed over 12 times the permissible level of nitrate at 554 mg/l. Other places with widespread nitrate pollution are Mandya (767 water samples), Kolar (647) and Davangere (442 samples). Nitrate is known to affect infants in particular, reducing the blood’s ability to carry oxygen.

Heavy metals

Water samples in some areas also contained high levels of heavy metals: chromium was found in Bangalore’s industrial area Peenya, while arsenic was present around the gold mines in Raichur, and in Yadgir. Iron, chlorides and calcium carbonate have also rendered thousands of other drinking water sources non-potable, the survey found.

The groundwater quality survey was part of a national exercise taken up under the Rajiv Gandhi National Drinking Water Mission. The survey was guided nationally by the National Remote Sensing Centre.

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