CHENNAI: Thirty million litres a day. That is the volume of untreated sewage that flows into the major waterways in Chennai every single day, while groundwater extraction continues to exceed natural recharge, creating a widening deficit concentrated in key urban blocks in the city.
According to Neervazhvu.org, an integrated data monitoring platform built on data collected from government monitoring centres, around 30.7 million (3.07 crore) litres per day (MLD) of sewage is discharged into the Cooum, Buckingham Canal, Otteri Nullah, and the Ennore Creek inlet. Data on Adyar river is not included in this.
Cooum tops the list with about 10.8 MLD, while it is 10.6 MLD in the case of the Buckingham Canal. Otteri Nullah receives 7.9 MLD, and the Ennore Creek inlet 1.2 MLD.
Identifying specific discharge points as major contributors, it said Elephant Gate Bridge was the single largest source, releasing 3.04 MLD into the Buckingham Canal – nearly 29% of its total pollution load. Otteri Bridge point accounts for 2.47 MLD into Otteri Nullah, while Andrews Bridge point contributes 1.34 MLD into the Cooum. In North Chennai, the Ennore inlet carries the entire 1.24 MLD discharge into Kosasthalaiyar.
Parallel to this pollution crisis is the issue of groundwater stress. According to OpenCity 2024 data collated by Neervazhvu, Chennai consumes around 318 MLD of groundwater daily, but the recharge stands at only 255 MLD, leaving a deficit of about 63 MLD. This overdraft is highly concentrated in just three blocks, Ambattur, Tiruvottiyur, and Maduravoyal, which together account for nearly the entire shortfall.
Ambattur alone records a deficit of 41 MLD, driven largely by intensive extraction in its industrial estate. Tiruvottiyur follows with a 14 MLD deficit, attributed to stress on the coastal aquifer system, while Maduravoyal faces a 7 MLD gap due to rapid peri-urban expansion and limited piped water supply.
Although areas like Sholinganallur and Madhavaram show surpluses of around 10-11 MLD, these gains are geographically isolated and insufficient to offset the broader imbalance.
Madhavaram's aquifer remains among the most stressed in the city, with groundwater levels dropping to nearly 16 metres below ground level.
The implications of these issues are further compounded by flood risk. Out of Chennai's 200 wards, 14 have been classified under high or very high flood hazard zones. The 11 wards that fall in the "very high" category are in Tiruvottiyur, Royapuram, Anna Nagar, Teynampet, Kodambakkam, and Sholinganallur. Three other wards in Anna Nagar and Adyar are categorised as high risk.
Speaking to DT Next, Sundaresh Prasanna, founder of Neervazhvu.org, said the convergence of sewage mismanagement, groundwater depletion, and flood vulnerability points to a deeper structural issue in urban planning. Without coordinated intervention, ranging from sewage treatment upgrades and aquifer recharge measures to improved stormwater infrastructure, Chennai's water crisis is likely to intensify in the coming years, he warned.
30.7 million litres Daily sewage discharge into Cooum, Buckingham Canal, Otteri Nullah, and Ennore Creek inlet
10.8 MLD Cooum
10.6 MLD Buckingham Canal
7.9 MLD Otteri Nullah
1.2 MLD Ennore Creek inlet
3.04 MLD enters Buckingham Canal from Elephant Gate Bridge
2.47 MLD enters Otteri Nullah from Otteri Bridge point
1.34 MLD from Andrews Bridge point into Cooum
1.24 MLD from Ennore inlet to Kosasthalaiyar