An earlier Veeranam Lake project aimed at augmenting the city's water supply failed.
[3] The expanded Chennai Metropolitan Area (CMA) has nearly 4,100 water bodies, with a potential storage capacity of 150,000 million cubic feet.
The first proposal to tap water from Kortalayar river situated about 160 km northwest of the city was forwarded by Fraser, a civil engineer.
According to J. W. Madeley, a pioneer of Chennai water supply and sewerage system during 1914–1918, these were considered sufficient for an anticipated population of 660,000 in 1961 at a rate of 25 gallons per head per day.
Ground water resources in Chennai are replenished by rainwater and the city's average rainfall is 1,276 mm.
Water to the city's residents is being supplied from desalination plants at Nemelli and Minjur; aquifers in Neyveli, Minjur and Panchetty; Cauvery water from Veeranam lake; Krishna River from Andhra Pradesh; Poondi reservoir; and lakes at Red Hills, Chembarambakkam and Sholavaram.
With the expansion of the corporation area from 174 sq km to 426 sq km, which increased the number of wards of the Chennai Corporation from 155 to 200 and the number of zones from 10 to 15, MetroWater's customer base is expected to increase by an additional 1.7 million when the new areas are covered.
Similarly, MetroWater has to provide infrastructure to treat and dispose an additional 219 mld of sewage estimated to be generated in the merged areas.
Nine lakes cannot be rejuvenated owing to encroachments, including those in Valasaravakkam, Virugambakkam, Mogappair, Adambakkam, Kolathur, Senneerkuppam, Thalakancheri, Ullagaram, and Maduravoyal.
Once rejuvenated completely, the remaining lakes will have a combined storage capacity of 1,000 million cubic feet (mcft).
Sandy areas include New Washermenpet, George Town, Manali, Porur and Besant Nagar, where the water level stood between 5 m and 6 m in 2012.
Hard rock areas include Guindy, Perungudi, Taramani and Velachery, where the level stood at 6.5 metre in the same period.
[19] The water level and quality is monitored by the Metrowater from 145 observation wells spread across the expanded city.
[20] In 2012, the Chennai Corporation began work on construction of 5,000 rainwater harvesting structures in stormwater drains.
The plants take in raw brackish water from bore wells, store in tanks, and then purify before supply.
As the capacity of sewers was limited, during rainy days they became surcharged due to ingress of storm water.
With the JNNURM project, there was a capacity addition in the city and its periphery with the total volume rising to 486 MLD.
[23] A ₹4,862.1-million second tertiary treatment plant at Koyambedu with a capacity of 45 million liters a day (MLD) started functioning from November 2019.
This freed up nearly 25 MLD of freshwater from Chembarambakkam lake that had been provided for industrial use so far for domestic water supply.
Located about 225 km south of Chennai, the tank is situated in the tail of the Cauvery river system in the state as it gets the supply through the Vadavar channel from the Lower Anicut on the Coleroon (Kollidam) besides rainwater from its own catchment area.
According to the Policy Note of the State Municipal Administration and Water Supply Department for 2012–2013, MetroWater supplies about 765 MLD to domestic consumers in the city and about 65 MLD of water to bulk consumers such as adjacent local bodies and industries located in the Chennai Metropolitan Area.
The second desalination plant was commissioned at Nemmeli in February 2013 and the city got an additional supply of 100 mld of water.
[27] In November 2012, the state government sought permission from the Union ministry of environment and forests for environmental clearance to build a one-tmcft reservoir at Thervoykandigai in Tiruvallur district to augment drinking water supply for the city, which if realized, would become the fifth reservoir in the metropolitan region.
There is also a proposal to build a 400-MLD desalination plant to fill the present gap in water supply in the city.
[citation needed] In 2011, the Chief Minister ordered desilting of few more lakes in the metropolitan area at a cost of ₹ 1,300 million.
[31] In October 2013, the Ministry of Earth Sciences and the Tamil Nadu government proposed to set up a 10 MLD low-temperature thermal desalination plant about 40 km from Chennai.