Overflowing Modak Sagar water redirected to Tansa

Man with bright idea saves 50m gallons of drinking water a day

If the city gets through the next 12 months without suffering a severe water crisis despite what has been an extremely poor monsoon, citizens will have a retired civic engineer to thank. 

    Prakash Limaye, who retired from the BMC's Waterworks department earlier this year, is based 100 km from Mumbai and is single-handedly saving nearly 50 million gallons of potable water — enough for 1 million people daily — from flowing into the Arabian Sea every day. On an average, Mumbai consumes 750 million gallons of water a day. 
    The idea itself is a combination of simplicity and common sense — terms not easily associated with the civic body. 
    Located 22 kms apart, Tansa and Modak Sagar dams are chief sources of drinking water to Mumbai. With below average rainfall this season, the water level at the 19-sq-km Tansa lake on Tansa river has stayed well below the desired level. 
    On the other hand, the eight-sq-km Modak Sagar, situated on the banks of Vaitarna river, started overflowing last week, and the city would have lost millions of gallons of drinking water to the sea had it not been for Limaye's plan. 
    The pipeline connecting Modak Sagar to Mumbai passes through the periphery of Tansa. Limaye's plan involves opening up valves on the pipelines at points closest to Tansa, thereby enabling the excess water to flow into Tansa instead of being wasted. 
    There are 30 scour valves passing through Tansa, each capable of releasing an average of 10 million gallons of water into the lake. At the moment, the BMC is opening 5-8 valves a day — saving close to 50 million gallons of drinking water in the process every day. In all, 400 million gallons of water have been banked over the last eight days. 
    Limaye, who has built his retirement home just 2 km from Tansa, is helping sub-engineer Vilas Aher in the operation. These valves need to be opened and shut manually — in fact, with a wrench — every day. 
    "Modak Sagar fills up quickly and overflows when there is a consistent rainfall of 900 mm, while Tansa requires around 1300-1400 mm of rainfall to fill to the brim. This year, we realised that it would be difficult to fill Tansa, so we proposed that the valves of the pipes that pass on its periphery be opened up," Limaye said. 
    "We have opened up five scours of the pipe coming from Modak Sagar towards Tansa and also stopped the water supply (daily share of 100 million gallons) from Tansa. As a result, the level of Tansa goes up by a foot (0.33 metres) daily. Each day, nearly 50 million gallons of water gets transferred from Modak Sagar to Tansa," Aher said. 
    Limaye, incidentally, had drawn up this blueprint in 2009, but a delay in getting the required approvals ensured that it was too late by the time the idea was implemented. That year, the city had to face acute water shortage, with the BMC imposing 15 per cent cuts on residential consumers. 
    With adequate rainfall in the next two years, the idea was as good as shelved. But with the monsoons barely registering, Limaye was at hand to prevent the taps from running dry.

Prakash Limaye, who retired from the BMC's Waterworks department earlier this year