CHENNAI: Nearly 7.5 crore litres of sewage and sullage are flowing every day through 65 open drains in 18 urban local bodies around Chennai, with most of the wastewater ultimately ending up in rivers, lakes, open grounds and other discharge points, according to data from the municipal administration and water supply department.
Tambaram accounts for the largest share, with seven open drains carrying about 35 million litres per day (MLD), all of it listed as ultimately discharging into the Adyar river. Kancheepuram has five drains carrying 13.4 MLD and Avadi has four drains carrying 11.7 MLD discharging in the Cooum.
Together, Tambaram, Kancheepuram and Avadi account for 60.1 MLD, or more than 80% of the total sewage and sullage carried through the identified drains.
In Kundrathur, three drains carrying 1.3 MLD are also linked to the Adyar river, while two drains in Nandivaram-Guduvancheri carry 0.618 MLD towards the Adyar River zero point. Madurantakam accounts for another 2 MLD through four drains, Thirunindravur 1.82 MLD through five drains, Minjur 1.8 MLD through six drains, Mangadu 1.6 MLD through four drains and Tiruttani 1.53 MLD through three drains.
Three drains in Poonamallee carry 920 kilolitres a day and two in Thiruverkadu carry 790 kilolitres. The department has said action plans have been taken up to stop sewage and sullage from entering the open drains and that discharge from all the identified local bodies would be arrested by December 2028.
The figures highlight the gap in underground sewerage coverage in the rapidly growing suburbs. An RTI reply had earlier shown that sewage from around 35% of buildings in Tambaram and Pallavaram reaches storm water drains and lakes.
Areas such as Chitlapakkam, where layouts were approved decades back, still do not have a complete underground sewage network.
Within Chennai city, a separate sewage-conveyance problem has also been adding to pollution in the waterways. Government data reported earlier showed that 150-180 MLD of sewage pumped from sewage stations fails to reach treatment plants every day and instead enters storm water drains before reaching the Cooum and Adyar rivers, and Buckingham Canal.