Chennai’s water woes worsen as reservoirs dry up and groundwater levels decline

Of the 51 revenue blocks in Chennai where groundwater is extracted, 46 are over-exploited. How is the government addressing this problem?

The devastation that hit the coastal parts of Tamil Nadu and Chennai during the December 2023 floods still haunts the people affected here. Just five months later, the city is already staring at a potential water shortage.

Reservoirs serve as the main source of water supply to Chennai residents. However, Veeranam Lake reached dead storage on February 28th due to a lack of inflow from the Mettur dam. As of the lake storage report of the Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB) on May 27th, the reservoirs currently hold only 42.28% of their total capacity.

The CMWSSB proposes desalination plants as a solution to meet Chennai’s water needs till the onset of the southwest monsoon. However, experts point out that the focus should be on improving the groundwater table.

While the Water Board claims that they have sufficient water to supply the city till August end or the first week of September, this only signifies that we continue to depend on the southwest monsoon, despite having good rainfall during the northeast monsoon.

lake storage
The data from CMWSSB shows that Chennai had overall storage of 7,300 mcft last year during the same period, while it only has 5,590 mcft this year. Pic: CMWSSB

Read more: Irregular water supply not just a seasonal issue for many Chennai families

Reservoirs cannot be the only source of drinking water supply to Chennai

Reservoirs serve as the primary source of water supply to Chennai now. Jayshree Vencatesan, Managing Trustee of Care Earth Trust, says that the reservoir system is geared only towards capturing the water temporarily.

The reservoirs are not natural sources of water but are man-made. “A lot of engineering, science and intelligence goes into the building reservoirs. The only stable wetlands in Chennai that are not tampered with in terms of loss of area or connectivity are the reservoirs,” says Jayshree, adding that we cannot expand the reservoirs but we can evolve a standard operating procedure to maintain them.

Harris Sultan SA, a water expert from Arappor Iyakkam, recalls that the government planned to desilt the reservoirs of Chembarambakkam, Red Hills, Poondi and Cholavaram for Rs 36 crore following the 2019 drought. The government had planned to remove 151.80 lakh cubic metres of silt.

“Removing the silt from these four reservoirs will help in storing around 1.9 TMC of water that will cater to Chennai’s water needs for around 45 days,” he notes, adding that the project never took off, as the plan was to execute it for eight years.

“All these reservoirs are meant to supplement drinking water supply and not to be the only source of potable water. Historically, people used wells and temple tanks for water,” adds Jayshree.

“Even if we create ten more reservoirs, it will not be sufficient to meet Chennai’s water needs,” she says, adding that the focus should be on improving groundwater recharge.

What does groundwater data say about Chennai’s water security?

Chennai is the first Indian city to have a comprehensive automatic groundwater monitoring system, introduced in 2021. There are 200 groundwater monitoring devices and 20 rain gauges across 15 zones in Chennai. The CMWSSB had installed these to assess the groundwater level across the city, so that the Board could take proactive measures when the groundwater table dipped.

“I have not noticed CMWSSB taking any effective measures based on groundwater data, unless they are doing it without anyone knowing,” notes Jayshree.

The data we accessed from the CMWSSB shows that five zones in Chennai have an average groundwater level from 4.5 metres to 6 metres. Meanwhile, the groundwater level in Zone 3, comprising areas like Puzhal, Madhavaram, Alex Nagar and Kalpalaiyam, is more than 6 metres deep.

Zone wise ground water level map
Zone-wise groundwater level map of Chennai. Pic:

Ward-wise data shows bad groundwater levels

Similarly, the ward-wise groundwater level data shows that three wards (32 Kalpalaiyam, 127 Virugambakkam North and 138 Kalaignar Karunanidhi Nagar) in Chennai have groundwater levels deeper than 12 metres; and nine wards (30 Alex Nagar, 56 Muthialpet, 58 Poonga Nagar, 71 Thiru Vi Ka Nagar, 79 Banu Nagar, 111 Thousand Lights, 122 Alwarpet (South) and 141 VOC Nagar) have groundwater levels between 9 metres and 12 metres. The groundwater level in 30 other wards is between 6 metres and 9 metres.

Ward wise groundwater level map of Chennai.
Ward-wise groundwater level map of Chennai. Pic:

What do these data sets mean for Chennai?

“Wells usually have water at 7 metres (25 feet) to 9 metres (30 feet) deep. Places where the water level is below 9 metres show there is no water in the well. This usually happens in drought conditions,” he says.

Chennai used to have a lot of wells. When the wells started drying up, people started relying on borewell water, which was dug to around 500 feet in many areas. Apartments drill borewells deeper than individual houses.

“When the apartment complexes install such deep borewells, it affects the adjacent areas and the water in wells in individual houses dry up faster. This forces the people in individual houses to buy water from private tankers for daily use,” says Harris, explaining a case study they did in Virugambakkam, where the groundwater level stands below 12 feet.

He also adds that there is no clarity if CMWSSB is trying to take the sub-surface water level data or the deep aquifers. “The numbers show that these are sub-surface levels that are usually taken from the wells. We need sub-surface level water. But this alone is not sufficient,” he notes.

Over-exploited water resources

Meanwhile, a government order from the Water Resource Department dated March 7, 2024 notes that of the 51 firkas (revenue sub-divisions) in Chennai where groundwater is extracted, only two (Puzhal and Sholinganallur) are safe. The other 46 are over-exploited, while three — Alandur, Madhavaram and Pallikaranai are in the semi-critical stage.

WRD groundwater data
A GO from WRD shows that of the 51 firkas in Chennai, 46 are over-exploited.

“When it is marked safe, this indicates that the groundwater has been recharged as much as it is extracted. When it changes to semi-critical, critical or over-exploited, it means that we are extracting the groundwater more than its recharging capacity,” explains Prabhakaran Veeraarasu, an environmental engineer and an activist from Poovulagin Nanbargal.

While the GO notes Sholinganallur as one of the safe groundwater extraction firkas in Chennai, Prabhakaran points out that areas like Sholinganallur in OMR might have a better groundwater level but the water may not be potable.

Despite having issues with the accuracy and the methods of taking the data on groundwater levels, the available data points out that the groundwater levels are depleting. “This also contributes to other natural disasters. We need to keep the earth wet and all our energy should be focussed on it,” says Jayshree.

“Having groundwater level data is important. But, it is more important to see what we do with these data,” says Prabhakaran.

What CMWSSB says

In an earlier interview with Citizen Matters, Managing Director of CMWSSB, Dr TG Vinay had said that desalination plants would bridge the gap in Chennai’s water needs.

Speaking on other solutions, he said, “As part of the decentralised water distribution policy, tertiary treatment ultrafiltration plants (TTUF) and water treatment plants (WTP) have been established around the lakes in Chennai. For instance, the treated water from the TTUF in Nesapakkam is let into the Porur Lake. This recharges the Porur lake. The water from the lake is taken to the WTP for redistribution to the city. We are now working towards enhancing our capacity to use treated water.”

On specific questions about the fund utilisation for desilting the reservoirs and measures taken to improve groundwater levels, we did not get a response from the CMWSSB MD.

Read more: Chennai just got a new system to monitor groundwater levels. How will it help?

The way forward

As per WHO norms, it is necessary to ensure 150 litres per capita per day. “When the freshwater need is about 5–10 litres per day, why should the government spend so much money and time on converting the water into freshwater?” asks Harris.

He suggests that recycled water need not be converted to freshwater. It can be used to recharge the groundwater by constructing wells near water bodies. The groundwater will automatically get recharged for all the areas near the waterbodies.

“People can take the recharged groundwater for use other than drinking from the wells or borewells. They need not depend on the government for this. The state can focus on supplying the water to areas that need the supply. This is a way towards self-sustainability. Unlike desalination plants, this is both economical and an environmentally-viable option,” he notes.

The depletion of groundwater levels clubbed with low water capacity in reservoirs even before May-end will affect vulnerable communities the most. It will take a heavy toll on their standard of living. The State government needs to take proactive measures to make the city water secure. Else, the residents, especially the vulnerable population of Chennai will have to pay a huge price.

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