S.Z.
I would put something within his reach at night so he can get his own drink. In general, kids call their parents to do this because they're bored, or lonely, or just want somebody to be at their beck and call. Is he in a crib, or bed? If he's in a bed, put something - water bottles, juice boxes, whatever - on his night stand. If he's in a crib, put it outside the crib but reachable. Let him know that this is all he'll get - he can't call you to say he needs more. At his age and older, everybody learns how to get through the night without feeding themselves or getting a lot to drink - he will, too. When he's old enough to go potty, it should actually be simpler - with a stool in the bathroom, he can get his own drink AND go potty.