Offering ice chips is good. Putting some water on your fingers and dabbing some on his lips to start getting him to lick it off might get him started too. Also if you have some apple cider vinegar, a tsp to his water, flavors it some that might entice him to drink. The vets that I have worked for have recommended this as well.

It is not unusual coming out of anesthesia to not want anything, but keep trying. He may feel more like by tomorrow but do call the vet tomorrow if still does not have anything by then.