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Use the next two months to save up water for a year  


Mumbai: The monsoon is still a couple of months away, and it’s too soon to buy a new umbrella or those plastic shoes. But there’s another kind of pre-monsoon preparation to be done, one which will reap rewards for the rest of the year—rainwater harvesting.
   Indeed, this is the time of year for members of cooperative housing societies to set aside their differences and loosen their purse strings for a simple procedure that will save them lakhs of rupees in water tankers. Asian Paints at Mulund has done it successfully, as have Powai’s Larsen and Toubro, Hiranandani Gardens and sundry residential projects across the city. “Installing a harvesting system in your building won’t even take two months,’’ says architect Nandan Mungekar, who has helped 250 buildings across the city put in one.
   The surgery is simple. All it requires is piping down from the rooftop to the ground and trenches along the compound wall to direct water towards the borewell, or if one wishes, a separate tank. A small pressure well and filtration chamber to clean the water before it passes into the well, and voila—the society is all set to harvest thousands of litres of water during the rains. “All we do is imitate the action of the hills, where all the rain falls and drains down to the lake. We have to find the hill in the ground,’’ says Mungekar.
   The economics is compelling. Buildings have found that they save up to 45 litres per day per head, which is about the amount used by a person for flushing the toilet. It’s also just a little less than one-third of the water that the municipal corporation provides every person every day in the older buildings. Given the price of a tanker these days, the one-time investment of Rs 1 to Rs 2.5 lakh seems paltry for such permanent profit.
   On a city-wide scale, the results could be astonishing. According to BMC officials, even if we decide to resort only to rooftop rain water harvesting, assuming 50% of the developed area to be roofed, we can very easily harvest 589.34 million litres a day (MLD). That would halve the city’s 1,000 mld water shortage—the BMC supplies about 3000 MLD, and the city’s demand is about 3,900 MLD.
   Even if it’s not possible to dig a tank because your building is on rocky ground or close to the sea, a water recharging structure will help keep the saline water at bay, and this will also help stop the building foundation from getting corroded, says Rudolph D’Souza of the Eureka Institute of Environment.