Every day, Mumbai generates millions of litres of sewage that, if properly treated and recycled, could have helped ease the current water shortage. Practically all of it goes into the Arabian Sea, giving it a stink and a brackish colour, when citizens could have used it for various purposes.

Treatment of sewage has been neglected over the years, with the need never felt as it is now. “In ideal conditions, around 20 per cent of the total water supplied can be recycled and used in Mumbai, but no one really thought about it until the crisis hit us,” said a civic official. “This will save a huge amount of drinking water and can cut down the demand-supply gap drastically.”

Of the 2,770 million litres distributed daily, 80 per cent turns into sewage water. Of the 2,600 million litres per day (mld) of sewage generated, 1,600 mld is treated primarily. Around 600 mld of that could have been treated further and put to various uses; in fact, 350 mld is already being treated well enough for non-potable purposes by commercial and bulk users, but even that is being wasted.

Only 30 mld water is being recycled while the rest is released into the sea after primary treatment,” said deputy chief engineer (sewerage operations) S S Palav. The 30 mld is being used for flushing toilets, cooling of air-conditioners and gardening.

Now there is a demand for the wasted sewerage. The lush green meadows of the Royal Western Turf Club of India (RWITC) and Wellingdon Club at the Mahalaxmi Racecourse have demanded 3 mld treated sewer water from the civic body. A 5-mld plant will be set up at the now defunct Gorai dumping ground to green the area.

A Mumbai citizen gets 90 litres everyday from the BMC but needs only half of that for drinking and cooking. “The remaining 45 litres gets spent on non-potable uses, including flushing and washing. The fresh drinking water used for such purposes can be saved if replaced by treated sewerage water,” an official said.

The sewerage department says any building of 2000 sq metres can set up a small grey water recycling plant and set up an additional pipeline for flushing of toilets. Water from the tank can be drawn for washing vehicles and gardening too.

Treatment makes sewer water 95 per cent pure. The BMC spends around Rs 10 for treating 1000 litres of sewer water per day, while the same amount of fresh water can be treated at only Rs 3.50.

Desalination is costlier, Rs 50-60 per 1,000 litres, besides an estimated capital cost of Rs 10 crore for setting up a plant of one mld. The civic administration is studying the feasibility of setting a 5-mld plant at Colaba in the next six months.

Treat it right
1972 Year when city first treated sewage water, with Air India Building at Nariman Point setting up a plant to process 0.225 mld and using the water for air-conditioners and toilets. Oberoi Hotel (0.30 mld), Mafatlal Building (0.125 mld) and State Bank of India (0.125 mld) followed in 1974. Botanical Garden in Colaba, RCF and Bakhtawar Towers also recycle sewage water.
23 Number of Indian cities that recycle sewage water for irrigation and other non-potable uses. Include Indore, Nagpur, Patna, Chennai, Anand, Pune, Chandigarh and Bhopal.
3 of the few countries that treat sewage water for drinking are Singapore, Australia and the US.