My son was the same way, I have read different things but our Dr. checked his glucose which that can be a sign of a probelm with, my sons was normal but you might want to look into it.
My son is 4 and he does the same thing. If I would give it to him he will take it and drink it in 2 seconds. I started only giving him low sugar juice and water nothing else. If he is wetting himself I would quit giving him a drink everytime he ask. Give him one cup and tell him when you drink it is gone. You will get no more till lunch, supper, ext. Split it into reasonable times. If my son says in between times he is thirsty he will get 1-2 drinks and he is fine with that. As long as you dont think it is medical. But most kids will take what you give them. My son would eat candy, chips ext. all day long if he could.