About 290
He has one 5 gallon and another at about 3.5 gallons, giving him 8.5 gallons of water total. In ounces (128 x 8.5) thats 1,088. From here, divide his total amount of water, 1,088 ounces, by the amount going into each cup, 3.75 ounces, resulting in 290.133, would would be rounded down because you don’t have that last full cup of water.