Fill up some empty 2L soda bottles and put them in the fridge if you have some extra space. Buy a few cases of Trader Joes 1.5L bottled water and put 'em in the closet. Each case is around 4.7 gallons I think. Fill up some used water bottles and put them in the freezer. You could quickly put up about 20-30 gallons and not even know its there.