drink ITEM
This will consume the ITEM and satiate some of your thirst. If you're unable to determine what type of drink you have, entering drink drink generally works.

drink LIQUID from CONTAINER
It is possible to carry a flask or a bottle of liquid.

drink water from BODY OF WATER
Some ponds, pools, springs and even fountains can help to quench your thirst.

Note: Alcoholic beverages do not help quench your thirst and will indeed get you drunk. You can view your intoxication status on your score card. When you reach 100% intox you will fall unconscious. Intoxication levels can affect things such as your ability to steal, or be stolen from.