Where does the water in your tap come from?

UNDERSTANDING WATER SUPPLY

Chembarambakkam Lake, one of the waterbodies from which metro water department sources water to the city. Credits: Wikimedia Commons

Just like all civilizations, Madras also drew sustenance from a river. Historically, Adyar and Cooum Rivers played a pivotal role in the flourishing of Chennai. But today, with these rivers polluted, Chennai is largely dependent on the Northeast monsoon (mid-October to mid-December) that recharges groundwater. The presence of hundreds of lakes and temple tanks is a silver lining, but with most of them encroached and polluted, they don’t meet the water demand of the ever-growing city.

So how exactly does this city of roughly 11 million people sustain itself?

Where do you get the water that flows in your taps every day? 

Three main water sources of Chennai

Chennai Metro Water Supply and Sewerage Board (CMWSSB), the nodal agency for water supply in the city, relies on three sources: surface water sources, groundwater and seawater desalination. 

Poondi, Redhills, Cholavaram, Chembarambakkam and Veeranam lakes are the surface water sources situated around 200 km from Chennai. In addition, the city also relies on water from neighbouring Andhra Pradesh (Telugu Ganga project), where water from Krishna River in the Srisailam reservoir (400km away) is diverted to Poondi reservoir.  

Last year, Metro water explored alternative sources, tapping water from Porur Lake, Retteri Lake, and the quarries of Erumaiyur and Sikarayapuram.

The two TTRO (Tertiary Treatment Reverse Osmosis) plants at Koyambedu and Kodungaiyur treats the sewage water generated in the central and western parts of the city. The 90 MLD (45 MLD in each plant) treated water is supplied to industries, thus reducing the burden on the surface water bodies. 

Both surface water and groundwater sources are largely dependent on the annual rainfall. The unprecedented drought in 2019 starkly underlined how rainfall affects the availability of water from these sources.

Water from river basins and borewell water from the irrigation fields of Kancheepuram and Tiruvallur are the primary sources of groundwater procured by the Metro water department. This is useful to meet the water demand in localities such as OMR and ECR, where groundwater is hard due to their proximity to the sea.

Subsurface water sources (lakes and tanks) from the rest of the Chennai Metropolitan Area also contribute to the city’s water supply. The two desalination plants at Nemmeli and Minjur are additional sources. 

The following table roughly explains water sourcing for Chennai:

1. Surface water sourcesPotential yield (in MLD)Available in good years (in MLD)
a.Poondi, Red hills, Cholavaram and Chembarambakkam250125
b.Telugu Ganga project930400
c. Veeranam lake*180100
d. Retteri Lake105
e.Porur Lake**1010
f.Quarries of Sikarayapuram and Eraimayur**4040
2. Ground water/ Sub surface water
a.Northern well fields and southern acquifier10025
3.Sea water desalination
a.Minjur and Nemmeli plants200200
Info source: CMWSSB

*When Veeranam lake goes dry, Metro Water department sources water from Walajah lake, that receives water from the Neyveli Limited Corporation.

**Water from the quarries and Porur lake are being sourced only from last year.

Treatment and supply

The water thus sourced by the CMWSSB goes through various levels of treatment before it reaches the end consumer. Treating the water removes or reduces contaminants in it. Chennai has water treatment plants that treat the water from surface water and ground water resources. Water reaches these treatment plants through lined conduits and arch conduits.

Designed capacity of treatment plants

  • Kilpauk water works – 270 MLD
  • Redhills treatment plant – 300 MLD
  • Chembarambakkam treatment plant – 530 MLD
  • Minjur desalination plant – 100 MLD
  • Nemmeli desalination plant – 100 MLD
  • Vadakuthu plant – 180 MLD
  • Surapet plant – 14 MLD

From the treatment plants, water is transported through 1000-mm diametre transmission mains (pipelines) to the 18 distribution zones in Chennai. There are three transmission mains in the north, central and southern part of the city to transport treated water from the plants to the water distribution zones. From these zones, water is supplied through pipelines and tankers to the households.

Other sources

Chennai’s water requirement is 850 MLD. Despite procuring water from the sources mentioned above, the Metro Water department cannot meet this demand entirely due to a host of reasons.

“Water supply from the metro water department varies from 700 – 830 MLD, depending on the water levels in the surface and ground water sources,” explained V G Ramaswamy, Superintendent Engineer, CMWSSB, adding that areas added to Chennai limits, such as Ambattur, Alandur and Thoraipakkam, are yet to get water connections.

A borewell in Adyar. Pic: Laasya Shekhar

Of the 12.5 lakh houses in the 426 sq km of Chennai, around 7.20 lakh houses have Metro Water connections. Due to the irregularity of supply, even the households with connections often rely on alternative water sources (open wells, borewells and private water tankers).

“The borewell culture emerged in the 1980s in Chennai to fill the gap between demand and supply in the city. In extended areas of Chennai, borewells are dug as deep as 800 feet, to extract water. The population rise in Chennai has far outstripped the availability of water resources, a prime factor behind the reduction in the ground water table,” said Hydro-geologist, J Saravanan.

As groundwater in coastal localities (Adyar, Besant Nagar and Thiruvottiyur) is saline due to the proximity to the sea, open wells are commonly witnessed.

When water from local borewells and open wells also dry up, citizens rely on private water tankers that again draw water from the river basins and fields of neighbouring districts. During the drought last year, private water tankers supplied 350 MLD water to the apartment complexes, individual houses and commercial spaces of Chennai.

2020 has been a water surplus year, but as ground water levels in Chennai are unpredictable and droughts are witnessed frequently, Metro Water is providing residential and commercial establishments with water meters. With or without water meters, though, it is the foremost responsibility of every citizen to save water by using the commodity judiciously.

(With inputs from CMWSSB and hydro geologist J Saravanan)


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About Laasya Shekhar 232 Articles
Laasya Shekhar is Senior Reporter at Citizen Matters Chennai. She tweets at @plaasya.

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