Why Bengaluru\'s ground water is deep and dirty

BENGALURU: With 81 per cent of Bengaluru’s landscape covered with paved surfaces, groundwater recharge is vastly impeded. So when 45 per cent of the city depends on ground water, it should surprise no one that bore wells are plumbing new depths.

Dr T V Ramachandra of the Centre for Ecological Sciences at the Indian Institute of Science (IISc) says a major cause of the plunging of ground water depths in Bengaluru is the slow erasure of lakes from its landscape. Once upon a time, lakeside localities could strike water 200-300 feet. Then the depths went down to 600-700 feet and now in some places you have to dig as deep as 1900 feet.

“When we go so deep, we would have reached the natural geological strata and we get water with trace elements,” said Dr Ramachandra.

One of the primary reasons for contamination of groundwater is the sustained inflow of sewage in the vicinity of lakes. This reflects in the high concentrations of nitrates an heavy metals in the groundwater.

In Anekal for instance residents point to the relentless exploitation of groundwater by the water mafia. And builders of large projects use ground water rather than treated water from the sewage treatment plant (STP).  

Bengaluru receives rainfall of 700-850 mm per annum, which supplies barely 15 tmc ft of water whle the demand is of the order of 18 tmc ft. Dr Ramachandra says it is now highly imperative that rain water harvesting is mandatory for buildings, both individual and institutional. Also, rejuvenating lakes with scientific desilting would enhance their water storage capacity and enhance ground water recharge with cleaner water.