The phrase "gallon water" refers to a specific amount of water, equal to four quarts or 3.785 liters. It is commonly used to measure large quantities of water, such as in bottles or containers.
The device has a hefty gallon water tank, which allows it to operate for up to 12 hours on a single filling, and it should run quietly. (businessinsider.com)
It heats up in two minutes or less, and each fill of the 3/4 - gallon water reservoir provides 1.5 hours of steam power. (thespruce.com)
Plus, taking a shorter shower can save thousands of gallons a water per year. (longwaitforisabella.com)