TTW is water generated by treating sewage three times.

More than 95 per cent of the sediments are removed from the sewage during the treatment. Therefore, one can easily use it for washing and cleaning purposes.

If TTW is purified in an ultrafiltration plant or reverse osmosis plant, it can be used even for drinking purposes.

Tertiary treated water costs only Rs 25 per kilolitre as against Rs 60 per kilolitre for normal water.

At present, only Bengaluru International Airport Limited (BIAL) and Bharat Electronics (BEL) consume TTW in Bangalore.

The two companies are consuming around five million litres of TTW per day (MLD) The Bangalore Water Supply and Sewerage Board (BWSSB) has a 10 MLD capacity tertiary treatment plant at Hebbal and 60 MLD plant at Vrishabhavathy Valley.

Every day, BWSSB produces around 15 MLD of TTW and uses the surplus TTW for gardening and washing purposes.

BWSSB chairman PB Ramamurthy said, “We have written letters to BBMP (Bruhat Bengaluru Mahanagara Palike), BDA (Bangalore Development Authority) and Contractors’ Association, requesting them to use TTW for construction and gardening purposes.

But they have not responded favourably till now. If they start using it, it will help us conserve power and the ecology.

Moreover, it is much cheaper than other sources of water.” Ramamurthy added that BWSSB was also exploring the possibility of supplying TTW to four different points in the city through pipelines to encourage people to use it. “We can give it at Rs 15 per kilolitre if the users can transport TTW themselves,” he said.

At present, the city needs 1,200 MLD water. However, BWSSB supplies around 870 MLD water through its sources. The city would need at least 2,050 MLD of water by 2025. Hence, TTW is considered to be one of the viable alternatives, as all the existing sources of water would have been thoroughly tapped by then.