Drop Zone

The Brihanmumbai Municipal Corporation (BMC) supplies 3,100 million litres a day (MLD), a shortfall of 800 MLD. This can be easily overcome if all buildings harvest rainwater. There are two basic ways — using rain to recharge the groundwater table or storing rainwater and using it when needed. Usually, rainwater is piped from building terraces into a tank and stored.

Though the government has made rainwater harvesting mandatory for all buildings on plots over 1,000 sq mt, only 100-odd buildings com ply. “We don’t supply water for flushing toilets to buildings post-2002,” says S. Paralkar, of the BMC’s Rainwater Har vesting Cell. But experts say that the BMC has not implemented this threat, which explains the low numbers.

A three-member team was formed in 2002 to spread awareness about rainwater harvesting. The cell plans to open ‘rain centres,’ where basic information and guidance will be given. Four centres have been planned initially — the BMC training centre in Borivli, Kasturba Hospital and two other yet-tobe-decided locations.

On average, one person uses 45 litres every day for flushing. To turn this on its head, a family of five would save 225 litres per day if it opts for rainwater harvesting.

Consider another statistic. If all 2 metres of rainwater (total amount of rainfall Mumbai receives) is harvested from a building terrace which houses five flats of 1,000 sq ft, then water equivalent to 70 tankers can be harvested in one building alone. This, after assuming that 25 per cent of the water is not harvested! Examples of success abound. The BEST saves 30,000 MLD due to rainwater harvesting. Sea Line building at Union Park, Bandra, harvests rainwater too. Navin Chandra, who was involved in putting the system in place, says, “Since we are a small society, we have a holding tank of just 10,000 litres. We collect all the rain water on the terrace and around the building. We’ve connected the tank to a 70-ft-long channel which is six feet deep and three feet wide.” The water which overflows is used to recharge the ground water table. Two borewells help draw this water up. This water is used for non-drinking purposes and is equivalent to 100 tankers, which would cost over Rs 1 lakh. And just in case a need is felt for drinking water too, a small filtration unit has been fitted to purify the water. Here’s the real miracle: the project costs a mere Rs 7 lakh.

Kanti Apartment on Mount Mary Road, Bandra, is another example of success. With 180 flats, it faced a severe shortage for three months last year when the water pipes were being repaired. This year, it has a rainwater harvesting system in place. Says society chairman Suresh Mirchandani, “We have four pits, which provide us enough to wash cars, water the garden and fill the swimming pool.” With an investment of a mere Rs 3 lakh, the building’s water woes have vanished. “Now, we can change the water in our pool every day. This monsoon, we have in place a system to harvest 10,000 litres per day. This will solve our water problems for the next 10 years,” beams Mirchandani.