The coastal city of Chennai has a metropolitan population of 10.6 million as per 2019 census. As the city lacks a perennial water source, catering the water requirements of the population has remained an arduous task. On 18 June 2019, the city's reservoirs ran dry, leaving the city in severe crisis.

Although three rivers flow through the metropolitan region and drain into the Bay of Bengal, Chennai has historically relied on annual monsoon rains to replenish its water reservoirs since the rivers are polluted with sewage. With the population increasing over the decades, the city has faced water supply shortages, and its ground water levels have been depleted. An earlier Veeranam Lake project aimed at augmenting the city's water supply failed. However, the New Veeranam project, which became operational in September 2004, has greatly reduced dependency on distant sources. In recent years, heavy and consistent monsoon rains and rainwater harvesting (RWH) by Chennai Metro Water at its Anna Nagar Rain Centre have significantly reduced water shortages. Moreover, newer projects like the Telugu Ganga project, which brings water from rivers such as the Krishna River in Andhra Pradesh, have eased water shortages. The city has constructed a couple of sea water desalination plants to further increase the water supply, with the two functioning since 2010 and 2013, respectively. A third one has been planned. However, Chennai is expected to face a huge deficit of 713 million litres per day (MLD) as the demand is projected at 2,248 MLD and supply estimated at only 1,535 MLD in 2026. As of 2017, the total volume of water harvested was 339 mcft and groundwater recharge was 170 mcft.

The expanded Chennai Metropolitan Area (CMA) has nearly 4,100 water bodies, with a potential storage capacity of 150,000 million cubic feet.

History Year Volume of waterharvested (mcft) Groundwaterrecharge (mcft) 1893 1,335 667 1954 1,038 519 1973 689 344 2006 371 185 2017 339 170 Until the middle of the 19th century, Chennai city received water from shallow wells and tanks, such as the Nungambakkam tank, in the region. The first proposal to tap water from Kortalayar river situated about 160 km northwest of the city was forwarded by Fraser, a civil engineer. The 1.85-million project involved construction of a masonry weir across Kortalayar River at Tamaraipakkam and diverting the water into Cholavaram lake and further into the Red Hills Lake by means of a channel. This established the first scientifically designed water distribution system in the city. The primary works were completed in 1870, and in 1872, a valve house at Red Hills and a gravity-aided earthen supply channel to supply water were built. Within the city, water was delivered by gravity into a masonry shaft at Kilpauk, where the channel ended. From here, the cast iron mains of the city branched off to carry water to different parts of the city. 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. However, the need for further improvement was felt in 1936.

Estimates say that the expanse of water bodies in and around Chennai contracted from 12.6 square kilometers in 1893 to 3.2 square kilometers in 2017. There were about 60 large water bodies in the Chennai area at one time, but as of 2017, they have come down to just 28, most of which are small.

Primary water sources Chennai is entirely dependent on ground water resources to meet its water needs. Ground water resources in Chennai are replenished by rainwater and the city's average rainfall is 1,276 mm. Chennai receives about 985 million liters per day (mld) from various sources against the required amount of 1,200 mld. This demand is expected to rise to 2,100 mld by 2031. 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.

Supply of ground water to the residents and sewage management in Chennai is taken care of by the Chennai Metropolitan Water Supply and Sewage Board (MetroWater). As of 2011, MetroWater is catering for a population of 5 million. 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. As of 2012, MetroWater supplies about 830 million litres of water every day to residents and commercial establishments. Of about 800 mld supplied to the city, nearly 710 mld is transmitted through pipeline. It is estimated that the demand of the expanded city would be 1,044 mld. Similarly, MetroWater has to provide infrastructure to treat and dispose an additional 219 mld of sewage estimated to be generated in the merged areas.

Chennai, after having grown into a metropolis, is now the Chennai Metropolitan Area (CMA) for planning purposes. The CMA has 22 water courses, including three rivers, a canal, and four reservoir tanks. This also includes 16 minor waterways.

The city has three rivers flowing into the Bay of Bengal, namely, the Cooum, the Adyar, and the Kosasthalaiyar, which divide the city into north–south sections. The Buckingham canal connects all the three rivers.

There are four reservoirs in the city, namely, Red Hills, Cholavaram, Poondi and Chembarambakkam, with a combined capacity of 11,057 mcft. The Red Hills reservoir has a capacity of 3,300 mcft. The Cholavaram reservoir has a capacity of 881 mcft. The Poondi reservoir has a capacity of 3,231 mcft. The Chembarambakkam reservoir has a capacity of 3,645 mcft. The reservoirs lose 5 mcft daily due to evaporation. A fifth reservoir is being planned.

According to the records of the Water Resources Department, only 19 of the 29 major waterbodies in the city's periphery can be restored. 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). In addition, if the four primary reservoirs are desilted by a metre, an additional water volume of about 500 mcft can be stored.

The city supplies 830 million litres of water per day. The city will get additional 1030 mld from sources such as Minjur desalination plant (100 mld), Krishna water (500 mld), Nemeli desalination plant (100 mld), Nemeli desalination plant-2 (150 mld) and Cauvery water from Veeranam Tank (180 mld). In 2026 planned to get another additional 400 mld from Perur Desalination Plant which is the fourth Desalination Plant in the City.

By December 2013, with the Nemmeli plant's contribution going up from 80 to 100 MLD, the desalination plants in Nemmeli and Minjur and the new Veeranam project contribute more than 60 percent of the city's supply, which then was 575 MLD.

It is estimated that as many as 3,600 tanks in and around the Chennai metro area (covering the whole of Kancheepuram and Tiruvallur districts), if properly preserved and networked, can provide five times the quantum of water that the city needs in normal times. Water harnessed through these tanks is estimated to be about 80,000 million cubic feet (TMC).

As of 2018, nearly 50 to 60 percent of the water supplied in Chennai and its suburbs is through private water tankers, which supply about 20,000 tanker loads of water every day, sourced from areas such as Mambakkam, Tiruporur, Poonamallee, Ayapakkam, and Manjambakkam. About 80 percent of households in the Chennai Metropolitan Area consume packaged drinking water. About 20 million liters of packaged drinking water are sold in the city daily.

Management of the resources

Water level and quality The water level varies between different regions of the city, such as sandy, clay, and rock areas. 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. Clay areas include Kolathur, Pulianthope, Ambattur, Sholinganallur, K.K.Nagar and Virugambakkam, where the level was at 5.5 m to 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. Unlike sandy area, recharge and dip in water level in hard rock areas is faster. The water quality too varies across the city. In 2012, the level of total dissolved solids ranged between 600 parts per million (ppm) and 1,500 ppm across the city against the permissible limit of 500 ppm.

The water level and quality is monitored by the Metrowater from 145 observation wells spread across the expanded city. As of 2012, the average water level in the city ranges between 5 and 6 metre. The water level dips to its maximum during June when there is not much recharge. The level raises to a shallow depth of 1.5 m to 2m in January, immediately after the northeast monsoon.

Although Chennai scores high in the working ratio in water utility, a measure of their operational efficiency, financial health and stability, compared to most of the other Indian cities, it still shows a poor working ratio, according to a study by Ernst & Young.

In 2012, the Chennai Corporation began work on construction of 5,000 rainwater harvesting structures in stormwater drains.

Treatment plants Chennai has reverse osmosis plants, namely, at Velachery, Nochikuppam, Kasimedu, and Ayodhyakuppam. The plants take in raw brackish water from bore wells, store in tanks, and then purify before supply.

Water treatment plants are located at Kilpauk (270 mld), Puzhal (300 mld), Vadakuthu (Veeranam Lake source) (180 mld), and Chembarambakkam (530 mld).

Sewage management

Sewage As of 2019, Chennai generates 550 million liters of sewage every day. The sewage system in the city was designed in 1910 for an estimated 1961 population of 660,000. Some modifications were in 1958. A comprehensive improvement to the city sewerage system was designed in 1958 for an estimated 1976 population of 2.55 million and a 1991 population of 2.72 million at a sewage flow rate of 110 lpcd in 1976 and 180 lpcd in 1991. The city was divided into five zones with proposals for five independent disposal works. It was planned to isolate the system of collection, transmission and disposal of sewage in each zone in order to obviate the difficulties of the relay system. Presently, the sewerage network in Chennai city has covered 98 percent of its old area covering 174 sq km. As the capacity of sewers was limited, during rainy days they became surcharged due to ingress of storm water. Any surplus of sewage in excess of pumping stations capacity was drained into the nearby natural water courses of the city, namely, Cooum river, Adyar river, Buckingham canal and Otteri nullah.

Sewage treatment Until 2005–06, the total capacity of the sewage treatment plants in the city was 222 million litres a day. With the JNNURM project, there was a capacity addition in the city and its periphery with the total volume rising to 486 MLD. As of 2011, another two plants with a total capacity of 114 MLD were under construction.

Tertiary treatment plant In October 2019, a 45-MLD tertiary treatment plant began its operations at Kodungaiyur.