His remarks come in the wake of a letter written to him by his Tamil Nadu counterpart Edappadi K Palaniswamy demanding the immediate release of 7 tmc feet of water to the state as per the final order of the Cauvery Water Disputes Tribunal.
"We do not have water. How can we supply to them? It is not possible to release water to Tamil Nadu," the Karnataka chief minister said in response to the letter.
"We expect a favourable order," he said on the hearing of the Cauvery water dispute next month.
Last week, the Supreme Court had indicated that it would deliver within a month its verdict on the decades-old water dispute between Tamil Nadu and Karnataka, saying enough confusion had been created on it for over two decades.
On the Mahadayi river dispute, Mr Siddarmaiah said a meeting would be called to resolve the matter at the earliest. The affected states will also be invited, he said.
The dispute over the sharing of water of the Mahadayi or Mandovi river between the states of Maharashtra, Karnataka and Goa is over 30 years old.