Under colonial rule, tanks were the only source of water in Mumbai. Many localities have been named after them. The BMC supplies potable water to the city from six lakes,[208][209] most of which comes from the Tulsi and Vihar lakes.[109] The Tansa lake supplies water to the western suburbs and parts of the island city along the Western Railway.[210] The water is filtered at Bhandup,[210] which is Asia's largest water filtration plant.[211] India's first underground water tunnel is being built in Mumbai.[212] About 700 million litres of water, out of a daily supply of 3500 million litres, is lost by way of water thefts, illegal connections and leakages, per day in Mumbai.[213] Almost all of Mumbai's daily refuse of 7,800 metric tonnes, of which 40 metric tonnes is plastic waste,[214] is transported to dumping grounds in Gorai in the northwest, Mulund in the northeast, and Deonar in the east.[215] Sewage treatment is carried out at Worli and Bandra, and disposed off by two independent marine outfalls of 3.4 km (2.1 mi) and 3.7 km (2.3 mi) at Bandra and Worli respectively.[216]
