When I know it's gonna be a long time before I hit another store to resupply, I carry as much as 2 1/2 gallons. I can carry 2 one gallon jugs and a gatorade in the bag that fits on top of my rack, 1 bottle on the frame, and sometimes a few small bottles in the panniers. It throws the weight out of balance a little going up hills and stuff, but it's easy to get used to.