With around one-fourth of Mumbai’s sewage being discharged untreated into the sea every day, the Bombay high court (HC) on Thursday directed the Maharashtra Pollution Control Board (MPCB) to ensure that the Brihanmumbai Municipal Corporation (BMC) takes steps to treat the same.A division bench of chief justice Pradeep Nandrajog and justice Nitin Jamdar directed the state pollution board to ensure the BMC installs, “within a reasonable period of time”, a network of sewage lines to bring the city’s untreated sewage to eight treatment plants.The directive came after senior advocate Anil Sakhare, representing the civic body, accepted that the disposal of untreated sewage into the sea is a problem primarily caused by lack of an adequate network of sewage lines. He also said the BMC had taken steps to address the problem.Sakhare was responding to a public interest litigation (PIL) filed by an NGO, Citizen Circle for Social Welfare and Education, complaining about the polluted coastal water, which is “dangerous to the entire ecosystem” and “makes the Mumbai shoreline one of the most polluted in the world”.According to the PIL, filed through advocate Shehzad Naqvi, and the MPCB’s submissions to the court, 93% of coastal water pollution around Mumbai is caused by the discharge of untreated sewage and waste directly into the sea, while 7% is owing to industrial effluents released in Mithi River and the creeks.The MPCB stated that of the 2,671MLD (million litres per day) of sewage generated in the city, 665MLD is directly released untreated into Mithi River and the sea, mainly owing to a lack of sewage lines connecting to treatment plants. Around 2,016MLD sewage is treated before being disposed in the sea, even though the eight treatment plants have a collective capacity to treat 2,595MLD every day, the MPCB submitted.The PIL also highlighted the fact that the water quality index (WQI) of the sea water at Juhu, Girgaum and Haji Ali were 44, 45 and 45.2, respectively, in October 2017, according to the MPCB. Water sample having WQI of 50-100 is considered nonpolluted, while below 50, the readings are considered polluted. The readings were 45.2 at Mahim, 46.1 at Worli Sea Face, 46.8 at Nariman Point and 28 (heavily polluted) at Mithi River.