Just 100 meters from the lake is a borewell, from where tankers draw their water and supply it without any purification. Samples tested at the Indian Institute of Science or IISC showed high levels of sodium concentration - 370 mg per litre. The safe limit, says the World Health Organisation or WHO, is 200 mg a litre. High levels of sodium in drinking-water increases blood pressure in children.
Seven borewells are seen next to the Sadaramangala Lake in the IT belt of Whitefield, which is equally polluted. Private tankers draw water from two - 6,000 litres for each of 50 trips.
Samples tested from one of the borewells showed high concentration calcium and magnesium, an excess of which is known to cause cardiovascular diseases. Against a permitted limit of 90.05 mg a litre, the calcium levels were 98.06 mg. The magnesium levels were 47.78 mg a litre against a permissible Limit of 43.87 mg.
Nearly 45 per cent of the city depends on groundwater. With the Bengaluru Water and Supply and Sewage board not willing to act as a monitoring body, and the local municipality also not interested, there is no regulator to check the quality of the water provided by the private water tankers. "We are not monitoring the quality of water, we want them to be registered with the BBMP as a commercial operator so that we are not affected if commercial establishments start preferring them over our supply," said Tushar Girinath, Chairman of BWSSB. The BBMP doesn't even have guidelines to regulate the water tankers.
IISC had surveyed 105 lakes in the city and published a report last year. Only four lakes were said to be in 'good' condition while the rest were getting untreated sewage, filled with macrophytes and solid waste was being dumped.
A study of ground water around Bellandur Lake by the Indian Institute of Science a few years ago shown a link between the ground water and the lake water quality. "We tested the borewell water and we found higher levels of nitrate," said Dr TV Ramachandra of the Centre For Ecological Sciences From Indian Institute of Science.
Residents, who didn't want to be identified, said local politicians are involved in the nexus and the impact on health is beginning to show. "Lots of people are suffering from skin allergies, especially children. We don't know where the water is coming from," said one resident.