The Supreme Court on 16 February 2018 reduced Tamil Nadu's share of Cauvery water and increased Karnataka's, instructing the latter to provide 177.25 thousand million cubic feet (TMC) water to the former.

Pronouncing its verdict on the decades-old Cauvery water dispute between the neighbouring states of Karnataka, Tamil Nadu, and Kerala, the apex court said given the global status of Karnataka's capital city of Bengaluru, it will get more Cauvery river water. Earlier, in accordance with the 2007 award of the Cauvery water dispute tribunal, Karnataka had a share of 270 tmcft of Cauvery water. This will now increase to 284.75 tmcft.
 
What
The judgement was pronounced by a bench of Chief Justice Dipak Misra and Justices Amitava Roy and A M Khanwilkar. Reading out the operative portion of the verdict, the CJI said the 2007 tribunal award of 30 tmcft to Kerala and 7 tmcft water to Puducherry will remain unchanged.
The apex court also allowed Tami Nadu to draw an additional 10 tmcft 'groundwater' from a total of 20 tmcft beneath the Cauvery basin. It said the increase in share of Cauvery water for Karnataka by 14.75 tmcft is because of the 10 tmcft groundwater and 4.75 tmcft drinking water requirement for Bengaluru residents.
Karnataka to provide 177.25 TMC feet water to Tamil Nadu instead of 192 TMC feet.  
No state can claim ownership over a river * Karnataka to get an additional 14.75 TMC feet
Earlier on September 20, 2017, the court had reserved its order on the matter. Tamil Nadu, Karnataka, Kerala, and Puducherry had filed petitions seeking modification of Cauvery Tribunal's final order.
Originally awarded 192 TMC water to Tamil Nadu has been reduced with SC order. 14.75 TMC extra water has been given to Karnataka to provide drinking water to Bengaluru city. 
It was in 1990 when the Centre created a tribunal to examine the conflict and address the water shortage. The CWDT had unanimously passed an order on how the water should be shared between the states after determining the total availability of water in the Cauvery basin.
Tamil Nadu has deployed hundreds of police personnel across Chennai city and towns bordering Karnataka. Top government sources said security has been tightened for all Karnataka establishments in the city.
Owing the geographic peculiarities of the State, Tamil Nadu has been dependent on water from the rivers in Karnataka and Kerala for a long time now. The dispute between Tamil Nadu and these two states also has a long history.
 
What
  1. A tribunal, constituted by the Government of India under the direction of the Supreme Court, came out with its final verdict in February, 2007, under which Tamil Nadu was entitled to get around 419 billion cubic feet of water, Karnataka, 270 billion cubic feet, Kerala, 30 bllion cubic feet and Puducherry was to get seven billion cubic feet of water, according to earlier reports.
  2. On October 18, 2016, the Supreme Court had asked Karnataka to release 2000 cusecs of Cauvery water per day to Tamil Nadu till further orders.
  3. On January 9, 2017, the Tamil Nadu Government had sought a compensation of Rs 2,480 crore from Karnataka for not releasing water to the state despite getting the Supreme Court directive to do so.