Water weighs about 8.34 lb per gallon about how many ounces per gallon is the weight of the water

The US gallon, which is equal to approximately 3.785 L, is legally defined as 231 cubic inches. A US liquid gallon of water weighs about 8.34 pounds or 3.78 kilograms at 62 °F (17 °C), making it about 16.6% lighter than the imperial gallon.

volume of water = 1 gal =.0037854 cubic meter

density of water = 1000kg per meter cube

weight of water =.0037854 * 1000 * 5 = 5 * 3.7854 = 18.927