CHENNAI: Untreated sewage continues to enter Puzhal Lake, one of Chennai’s most critical drinking water sources, highlighting persistent apathy on the part of the Greater Chennai Corporation in safeguarding a reservoir that supplies nearly one-fifth of the city’s daily water requirement.

With a full storage capacity of about 3,300 MCFT, Puzhal is a live reservoir feeding the city’s water grid. Of the around 1,230 MCFT currently supplied by the Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB), nearly one-fifth is drawn from Puzhal after treatment at the Puzhal water treatment plant, which supplies about 240 million litres per day to parts of north and central Chennai. Despite this, untreated wastewater continues to enter the lake through stormwater drains (SWDs) and open channels along the Ambattur stretch.

Residents in North Banu Nagar, Banu Nagar, Vedachalam Nagar and Kallikuppam describe sewage mixing into drains and channels near the lake as a regular occurrence. Several stretches are marked by a persistent stench. “Almost every day, sewage water overflows here. Officials come and go, but there is never a solution,” lamented a resident of Kallikuppam.

Beyond contamination, residents also point to the impact on daily living conditions. The foul smell is constant, forcing households to keep windows closed for much of the day. Insects breeding around the drains, particularly during evenings, have added to the problem.

Civic activist Jayachandran of Ambattur said that local practices have also contributed to the situation. “Wastewater from houses, eateries and small industrial units is often diverted into SWDs. Residents and local establishments must take responsibility too, as they are also a major reason for this. Repeated complaints to the Greater Chennai Corporation (GCC) had not resulted in a lasting solution,” he explained.

The Water Resources Department (WRD) has acknowledged the complaints of sewage discharge in Ambattur, particularly along the Manal Odai drain canal, and said the matter has been taken up with the GCC. It added that the source of sewage inflow into the lake requires further examination, as the drain’s shutters are typically opened only during rainfall.

The Madras High Court, while hearing a writ petition on January 5, took note of allegations relating to the mixing of sewage water with drinking water and directed the CMWSSB to report on the steps it would take if the allegations were found to be true.

VS Suresh, the advocate who filed the writ petition, pointed out the inadequate SWD system in parts of Ambattur, especially in areas where water has to be pumped from low-lying to higher elevations. “With the lake at full capacity, water backtracks and stagnates. This eventually leads to pollution of drinking water,” he added.

Following proceedings before the High Court in October 2025, the WRD formally flagged the entry of untreated sewage into major drinking water sources in Puzhal Lake. The department’s communication identified problems across parts of the Madhavaram Zone, adjoining panchayat areas in Tiruvallur and Ambattur.

The SWD department, however, said there had been no lapse in oversight, maintaining that monitoring had been intensified and fines were being imposed wherever violations were detected.