MUMBAI: It's an innovative solution to the water crisis that's threatening to cripple Mumbai. What's more, it isn't only in the realm of theory, a few hundred Mumbaikars have already started acting on it.

Here's the theory part: If the five million-odd denizens of this city who live in residential complexes transfer half their flush tank water into plastic bags or bottles and put these into the tanks, hydraulic experts in the city confirm that the city will jointly end up saving more than half the water that Tansa supplies to the city daily, and more than Tulsi and Vihar's per day supply put together. Additionally, almost two days of the city's entire water supply will be saved if this practice is continued for a month.

The BMC supplies water to a slum population of approximately seven million. The remaining water goes to a population of over five million people living in residential complexes, where the average flush capacity is between 7 and 10 litres. Now, assuming a person uses the loo eight times a day, s/he flushes a minimum of 56 to 80 litres in 24 hours. Experts, who were civic hydraulic engineers in the past, say that reducing this usage by half in the manner mentioned can save a great deal of water: 30-40 litres of water per household per day, and 150-200 million litres for the city. At the end of the month, the savings amount to 6,000 mld, which is almost two days of Mumbai's water supply.

If certain BMC engineers are to be believed, hundreds of families in the western suburbs are already practising the half-flush tank method. Sure, they're doing it to tide over their own water crisis, but the city benefits by default. Aniruddha Ghanekar's family and their neighbours in Bandra East's Gandhinagar have put plastic bags containing over four litres of water into their 10-litre flush tank. This, Aniruddha, a civil engineer by profession, says helps them "save half the quantity of water from the overhead tank they use for flushing for over seven times a day''.

A few apartments in Chembur, Goregaon and Andheri, where Ghanekar's friends and relatives live, have also followed suit.

An increasing number of Mumbaikars have been resorting to this method ever since the water cut came into force. The BMC's hydraulic engineers, while lauding the idea which has been propagated by environmental NGOs for years, refuse to officially ask people to adopt it. Says Pramod Guhe, one of these engineers, "It is good that people are at least toying with several options to save water. Ideally, people should replace flush tanks with a capacity of 7-10 litres with those of 3-5 litres, which is adequate.''