The total amount of water in an average adult human body is four gallons.

The given statement is false.

Explanation:

The average water, which an adult human body comprises is 60 percent. Thus, one can find the average water content by getting 60 percent of an individual's body weight with the units of kilograms and liters respectively.  

For example, let us consider that the average adult in the United States weighs 88 Kgs. Therefore, 60 percent of that value is 52.8 liters, and if transformed into gallons, the outcome will be 13.9. Thus, one can say that the given statement is false.