A Supreme Court order directing Karnataka to release water from the Cauvery river to Tamil Nadu has led to riots in Bengaluru, and some trouble in Chennai too. The violent response is largely because of the dependence of the two capitals on the Cauvery for their drinking water needs.

What appears to be a below-normal monsoon this year has resulted in a considerable drop in the water levels of reservoirs and dams in Karnataka. In this backdrop, the state feels sharing water with Tamil Nadu will result in a drinking water crisis in its southern parts, and especially in its capital.

Across the border, Chennai banks heavily on the Veeranam lake, 180 km away in the northern district of Cuddalore, to quench its thirst. This lake is fed by Cauvery water released from the Mettur dam, the point where the river enters Tamil Nadu in Salem.

But how did the two cities became so dependent on a river that has increasingly become undependable? A large part of the answer lies in the way they have let their own water bodies decline. Many of the lakes, tanks and wetlands in the two capitals have disappeared, swallowed up by encroachment and rapid development.

Price of Bengaluru's development

In September last year, the National Green Tribunal pulled up the Karnataka government for showing apathy in retrieving water bodies lost to development. The point it raised was telling: Bengaluru had 267 lakes in the 1960s but that number had plunged to 68 in 2015.

Called lakes, much of these water bodies were actually artificially created through the centuries for water storage and groundwater recharge.

According to Harini Nagendra, a professor in the School of Development at Azim Premji University, Bengaluru began drawing water from outside its territory at the end of the 19th Century, when the British ran out of space to build more tanks. The easy availability of water from outside meant the city’s own water bodies began losing their sacred position.

“Most of them were treated with reverence, but this reverence gave way to apathy once water was available from reservoirs outside,” she said.

The result of this was that buildings started coming up on lake beds and garbage was dumped into the lakes, slowly killing them.

The descent was rapid from the 1990s, when the city emerged as the country’s information technology hub and saw a manifold increase in its population. Slowly, the dependency on water from the Cauvery went up.

Bengaluru consumes about 1.5 thousand million cubic feet of Cauvery water a month, according to data with the state. One tmc feet works out to about 28.3 billion litres.

The city requires an estimated 1.5 billion litres of water a day, close to 45 billion litres a month. Apart from the Cauvery, it depends on groundwater to fulfil its needs.

Here comes the catch. Groundwater tables in the city’s densely populated urban areas have plummeted to 500 metres from 28 metres in the last 20 years, according to the June edition of the Current Science journal.

A field study of 105 lakes in and around the city showed 98% of them had been encroached upon while 90% of them were sewage-fed.

Since the demand for water will only increase with Bengaluru’s population estimated to touch 10 million in 2021 from 9.5 million now, the long-festering Cauvery dispute is bound to get uglier.

Chennai needs the Cauvery

In the rival capital of Chennai, the government has fared better in maintaining key reservoirs such as Poondi and Red Hills. Since the city sits on the coast, desalination – the process of turning salt water into water fit for human consumption – is a viable alternative, with plants such as the one in Nemmeli on East Coast Road already functional and being expanded.

However, this does not mean Chennai's dependency on the Cauvery will go down any time soon. The Veeranam lake supplies 180 million litres, or 18%, of the city’s daily requirement of 1 billion litres of water. Before the Veeranam project became functional in 2004, the city faced a massive scarcity of water in the summers, especially in drought years.

Tamil Nadu does not benefit much from the South West monsoon – an argument also presented by a Public Works Department consultant here, who said the allegation that Tamil Nadu seeks water for storage while Karnataka needs it for immediate use did not present the right picture.

"The North East monsoon is not consistent. What if it fails?,” he asked, adding that storage in September was crucial to meet both irrigation and drinking needs in case of a bad monsoon.

But like Bengaluru, Chennai’s water bodies, too, have suffered. One part of the Pallikaranai marshland, south of Chennai, has become a garbage dump while another part has been encroached upon by IT companies. The Maduravoyal lake has shrunk from 120 acres to 25 acres in the last two decades. Some 19 lakes have lost 500 hectares to development.

The floods that ravaged Chennai in December 2015, after the city received the heaviest rainfall in 100 years, were largely because of overflowing lakes choked by illegal construction.

Lessons to learn

It was the same story in Bengaluru in July this year, when its neglected lakes flooded large parts of the city.

And this ill-treatment of its water bodies is all due to the easy availability of water from the Cauvery, contended S Janakarajan, economist and professor at the Madras Institute of Development Studies.

“As the groundwater level goes down, Bengaluru will depend more and more on the Cauvery,” he said.

The IT city is expected to draw an additional 8 tmc feet of water from the river by 2021.

However, the academic said such a situation cannot become an excuse for Karnataka to deny water to Tamil Nadu, since the latter has a legal right to it.

What the two cities can do to avert a bigger problem is to learn from each other's mistakes and good practices. In Chennai, the groundwater situation is relatively better as the government has made rainwater harvesting compulsory for all buildings and has implemented the policy with all seriousness.

And the decline of Bengaluru’s lakes and tanks is a glaring lesson on how not to treat water bodies that are vital to a city’s welfare.