Five gallons of fresh water weigh 41.7 pounds, because each gallon of water equals 8.34 pounds. At the boiling point, a gallon of water has a weight of only 7.996 pounds. A cubic foot of room temperature water weighs 62.4 pounds.
However, salt water has a greater weight because of the minerals that are dissolved in it. Each gallon of sea water contains about 4.5 ounces of salt, which is about 3.5 percent of its total weight. A cubic foot of salt water weighs about 64 pounds. Because salt water is heavier, it is able to buoy objects up with a greater force, so objects float slightly better in salt water.