8-10 litres per week, skim milk only. I have no idea what that is in gallons but I buy 2 big jugs per week at least.
Milk is my one food addiction, literally.
I drink at least three glasses during the night and another two before going to work. I literally cannot go through 24 hours without a glass of skim milk. Maybe I need a 12 step program.

edit: just looked it up on the net and that would be 2.64 gallons (all by myself)