When it comes to sources of water supply, Adyar and Cooum rivers have played a significant role in contributing to Chennai’s source of drinking water and sustaining the population. The situation has changed drastically with these two rivers becoming highly polluted, unusable and the city depends exclusively upon the North-East Monsoon to recharge its groundwater. Chennai obtains its water from surface water, ground water and desalinated seawater. Poondi, Redhills, Cholavaram, Chembarambakkam lakes serve as surface water storage. It also relies upon faraway lakes like Veeranam and Krishna River in neighboring state of Andhra Pradesh. However, both surface and groundwater depend largely upon annual rainfall and are exposed to severe drought, like the one which occurred in 2019. The metro water department acquires groundwater from river basins and borewell in irrigation fields of Kanchipuram and Thiruvallur districts and is helpful in meeting the demands of the extended population living in OMR (Old Mahabalipuram Road – IT Corridor expressway) and ECR (East Coast Road). The desalinated seawater source comes from the two desalination plants in Nemmeli village along ECR and Minjur.
Chennai Metro Water Supply and Sewerage Board (CMWSSB), the nodal agency for the city’s water supply subject the water through different levels of water treatment, before using it for consumption. This removes or reduces contaminants. From the treatment plants, water is transported through 1000-mm diameter transmission pipelines to the various zones in Chennai. There are three main transmission lines in the northern, central and southern part of the city, that transports treated water to the distribution zones. Pipelines and tanker lorries supply water from these zones to individual households. There are seven treatment plants namely Kilpauk water works, Redhills treatment plant Chembarambakkam treatment plant, Minjur desalination plant, Nemmeli desalination plant, Vadakuthu plant and Surapet plant. Chembarambakkam plant is designed with a treatment capacity of 530 MLD and the lowest is Surapet plant about 14 MLD (Minimal Liquid Discharge). The tertiary treatment reverse osmosis plant at Koyambedu and Kodungaiyur treats sewage water generated in central and western parts of the city.