Diving really can dehydrate you, so being thirsty after a dive is normal and you should drink. I would say if you can, stay away from the soda (cola, sprite, etc.) and stick with some cool water. If you really can't deal with the water, apple juice(no sugar added) is a good second, and much better than other juices and such. There are mixed feelings about sports drinks, but I can't stand the taste anyway.

Remember, drink before your dive and after your dive. Everyone pees in the water (well not me, I dive in a dry suit and don't have a pee valve.....yet), so don't worry about that.