I have one gallon jug that I drink out of, and another backup gallon I keep in the cooler just in case. I also have 1-2 large whey/waxy maize/creatine shakes in the cooler that I sip as well between sets to keep catabolism at bay. I typically finish at least one of the gallons of H2O and one shake by the end of the workout. I may drink both of each if it's a particularly grueling leg or back workout.
I should mention that I also have a plate or two of chicken/rice or steak/potatoes in the cooler as well - I usually eat on the gym floor after I've completed my last set and I've already finished my shake - I don't want to miss that "window of opportunity" to shuttle those nutrients into the starving muscles ASAP. I find that the quicker acting nutrients in the shake chased down by slower acting solid food protein, fats, and complex carbs is a great help to postworkout recovery.