Five years ago, the Maharashtra Nature Park, near Dharavi, used to run up an annual municipal water bill of about Rs 3.5 lakh.
Today, the park never pays more than Rs 4,000 a year. It has stopped using civic water entirely, except for 1,000 litres a day used for drinking.
So how did the 37-acre park, which needs about 1 lakh litres per watering day just for its trees, manage to do this?
Well, they created their own water supply system.
The nature park lies between Dharavi and the Mithi river estuary. Along the estuary, the park has built a pond to store all the water it collects from — what else — rainwater harvesting.
“Rainwater collected on the 1,400-sq-metre roof of our main office building and 200-sq-metre courtyard is diverted to the pond, where it is stored all year round and from where it is piped across the park,” says Avinash Kubal, deputy director of the park.
The idea first struck Kubal in 2006, when he was crunching numbers and realised just how much water the park was using for ‘irrigation’.
“The BMC water supply is clean and potable,” says Kubal. “Now, you really don’t need drinking water for irrigation. So wasting lakhs of litres of clean, BMC water on our trees seemed criminal. That’s when I thought of rainwater harvesting.”
The nature park needs about 1 crore litres of water every year.
The pond — with a perimeter of about 260 metres, dug with the help of 4,000 National Service Scheme (NSS) volunteers — can store up to 2.25 crore litres.
“We have extra storage capacity to allow for losses from seepage and evaporation,” says Kubal.
Since the pond was built without using any cement, about 15 lakh litres of water seep every year through the large rocks that form its foundation.
“Another 20 to 25 lakh litres are lost to evaporation and we have to keep a dead stock of 30 to 40 lakh litres so we can run the pump,” says Kubal.
That leaves the park with an additional 45 lakh litres per year as an H2O contingency fund.
A small canal dug from the surface level to the nearby Mithi allows surplus water — yes, the tank often overflows in the monsoon — to find its way out.
“Thanks to the pond, the nature park only needs BMC water for drinking,” says Pramod Salaskar, who is heading a three-year state-appointed research project on the park. “I have been studying the pond and its water quality since May 2009, and it truly is a wonderful green initiative.”