Dehydration and Rehydration question?

I am very superstitious in basketball and today I shot 3/3 from 3-pt range and I finished with 13-15 points and I really don't shoot so well from downtown but this was just practice. Anyways I have a game tomorrow but i realized that before practice today, all I had was just 1 cup of milk and I want to be hydrated before the game. SO my question is "can i just drink a lot of water today (15 cups or so) and just have my 1 cup of milk tomorrow and still be hydrated? I'll drink 5 cups of water during the game but i don't want to risk my health because of my superstitions.