Despite acute shortage, city fails to tap the potential of rainwater harvesting systems
Shalini Nair & Hemali Chhapia | TNN
If the wars of this century were fought over oil, the wars of the next century will be fought over water - World Bank, 1995
Mumbai: For years, the 250 families of the 33-storeyed Avalon building at Powai continued to pay Rs 30,000 a month for tanker water. And then just before the rains this year, they invested in the crudest form of rainwater harvesting - connecting open pipes from the top of the building to an underground tank. Now, theyll save Rs 1 lakh every monsoon.
The Avalon experiment is proof of the vast potential offered by rainwater harvesting in a city reeling under water shortage.
Rainwater harvesting is a process of collecting the water that falls on terraces and rooftops during the monsoon and storing it in tanks, pits, trenches, bore-wells, etc. Estimates show that if Mumbai had conserved 20% of the rainfall received this monsoon with the help of rooftop harvesting alone, total water generated would have amounted to 600 million litres per day (MLD). Juxtapose this against the 550 MLD shortfall in the current supply and we realise the wonders water management can work.
With steady loss of open, green space and rapid concretisation, merely three percent of rainwater received by Mumbai now gets stored in lakes or as groundwater; the remaining 97% drains into the sea. Tapping any of it would require a very small investment.
It just cost us Rs 1.40 lakh. Throughout the year, we were dependent on three tankers a day. Now our demand is taken care of for at least the three months during the monsoon. Whats more, rain water is of a much better quality than the hard water we used to get in tankers, says Avalon resident Jaikumar Kamath.
Rainwater is indeed soft and low in salt content and impurities. It can easily be used for bathing, toilet-flushing, washing clothes and utensils and other non-potable purposes. The BMC has anyway stopped supplying water for flushing requirements and cut down water supply from 135 litres per person to 90 litres per person in all new buildings. So citizens in upcoming townships could easily meet this shortfall by implementing different kinds of rainwater harvesting techniques (see graphic).
Experts say harvesting using percolation pits for groundwater recharge can also help renew the water table in borewells. It is known that a lot of wells have gone dry, but because we are employing harsh methods of pulling water from the ground, using pumps, very often sea water seeps in. But underground springs can be renewed by harvesting rain water, which can stored for immediate or later use, said Rudolf Dsouza, trustee of Eureka Forbes Institute of Environment.
Assume that 70% of Mumbais area is developed, of which 50% is roofed and we collect 70% of the water falling over it, then the quantity of rainwater that can be harvested works out to 589.34 MLD (million litres per day). This is a sizeable quantity compared to the current water supply to Mumbai. In fact, a little bit of foresight and citizens participation could have helped the BMC save the whopping Rs 1,600 crore of public funds it will spend on the Middle Vaitarna project that will bring in 455 MLD additional water to the city by 2012.
But very few housing societies have made efforts in this direction and the state too has failed to promote the trend. Most buildings which started harvesting, have done so only in the face of acute shortage and due to excessive dependence on tanker water. Like Kanan Divecha, a resident of Kalyan Complex on Yari Road said, only after his building began facing problems in the late 90s, did they start researching about rainwater harvesting.
After all, when were born, were taught that water, like air, is a free commodity. Only in 2004, when our tanker bills touched Rs 40,000 did we call for a meeting to put in place a system of water harvesting, she said. Finally, when they calculated the amount of water that could be harvested 1,00,08,000 litres annually the residents realised they were sitting on an idea worth a million bucks.
In case you too find the argument convincing, you could start planning on a harvesting project that would be in place before next years monsoon.
( For free consultation on rainwater harvesting systems contact: Rain Water Harvesting Cell (BMC): 22620251 Extn: 2309 Asian Paints Total Water Management Centre: 25644191 Eureka Forbes Institue of Environment: 24301725)