Probably 1-2 gallons.
Partially because I use tea to keep me awake. Also because I tend to eat when I'm bored, and drinking a lot of water helps prevent that while tea helps fight the urge for sugary drinks.
1-2 gallons per day? I don't understand how that is possible haha. When I lived back home I used to drink up to half a gallon of milk and 2 cans of soda per day, was a decent way to gain weight fast, but it was also just so much.