Blame it on the way the city has developed in the last one decade that 70 per cent of the rainwater that Bengaluru receives goes waste. It does not percolate to recharge the ground water, but gets mixed with the sewage that flows into the lakes and rivers. Now that the rains are causing flooding year after year, environmentalists suggest redoing the valley network in Bengaluru connecting major water bodies.
Environmentalists have warned of higher water contamination in the river Cauvery flowing towards Tamil Nadu if water in storm water drains of Bengaluru is not treated before being released into the river. Research conducted by a team from IISc last year had pointed out that the reason for the profuse growth of water hyacinth in the Cauvery was due to the discharge of large amounts of sewage.
Senior environmentalist A. N. Yellapa Reddy says the sewage mixed rainwater from Vrushabhavathi Valley reaches Bellandur Lake in Bidadi taluk, and the same water later joins the Cauvery River after Kanakpura. "Similarly the sewage mixed water flowing from Chellaghatta Valley is spoiling the waters of the Yelemallappa Lake," Mr Reddy pointed out.
Mr C. S. Vedant, PCCF and former chairman of the Lake Development Authority, says that the drains in Bengaluru are old and changing the network is not an easy task. "Moreover, due to rapid urbanisation, there is no scope for water percolation. And rain water harvesting is not a success in Bengaluru still,” he said.