The amount of water bottle is 128 ounces in a gallon much more ies. If you are working with a bottle of water per liter, there are 3.785l per gallon. If you are working in US traditional units, divide 128 by the amount of water bottle. If you are working on a metric system, give the 3.785 option for tge 128. Your answer will be somewhere between 3 and 20.