Pointing to Indus Waters Treaty, Karnataka signals intent to revisit Cauvery water allocation

Account subscription benefits alongside Premium Stories, Editorials, Opinions and more. Unlock these with Subscription

An aerial drone view of water being released from the Mukkombu Upper Anaicut dam into the Cauvery River. File | Photo Credit: ANI

The State of Karnataka on Wednesday (October 7, 2026) signalled its intent in the Supreme Court to unravel decades-old judicial consensus on the Cauvery water-sharing dispute on the grounds of “inequitable allocation” of water and “changed circumstances”.

Even the Union of India has been seeking a modification of the now-in-abeyance Indus Waters Treaty of 1960 on the ground of changed circumstances, the State said.

Karnataka was replying to Tamil Nadu’s application in the Supreme Court, complaining of backlog in the allocation of the Cauvery water.

The State’s response, filed by advocate Nishanth Patil and settled by senior advocate Mohan Katarki, referred to international practices to revisit inter-State water allocations by agreement or adjudication in the changed circumstances, known as rebus sic stantibus .

“In view of the looming inequity, the State of Karnataka reserves its right to apply in the changed circumstances for reopening of the inequitable allocation in the Award of Tribunal read with judgment of the Supreme Court. The normal practice is that the water allocations are periodically revisited,” the 40-page reply said.

The tribunal award, along with the apex court judgment in 2018, had allocated the total annual flow of the Cauvery basin assessed at 740 tmc ft (thousand million cubic feet) at 50% dependability at Lower Coleroon Anicut. This water was apportioned between Karnataka (284.75 tmc ft), Tamil Nadu (404.25 tmc ft), Keralam (30 tmc ft), and Puducherry (7 tmc ft), alongside allocations of 10 tmc ft for environmental flows and 4 tmc ft earmarked as inevitable wastage to the sea.

In case the annual yield was less than 740 tmc ft in any water year due to distress caused by less rainfall, the States were directed to share distress proportionately ( pro rata ).

But Karnataka said there was no scientific formula for sharing distress on a pro rata or proportionate manner.

The present water year 2026-27 has been a distress one due to the failure of the southwest monsoon from June to September. Water-sharing was entirely based on a sense of equity, but hydrological realities have changed due to climate change, environmental degradation, shifting monsoons, etc. The water allocation and quantities decided by the tribunal, and confirmed by the apex court, followed a rigid pattern which had not taken any of these subsequent developments into consideration, Karnataka’s response said.

Water-sharing in a distress year has to take into consideration the absence of a scientific distress formula “as admitted by Tamil Nadu”. Secondly, the absence of a monthly component of annual yield of 740 tmc ft was also a factor, the response said.

Moreover, the Cauvery basin has two rainfall seasons: the southwest monsoon from June to September, and the northeast monsoon from October to December or beyond.