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