Dishwasher or Hand Washing?

A dishwasher often uses less water than handwashing with the tap running, but the result depends on the model, cycle, and washing method. EPA says ENERGY STAR models use no more than 3.2 gallons per cycle; “about 4 gallons” is a rounded estimate for a typical modern example. Up to 20 gallons for handwashing is an upper estimate for some habits, not a fixed amount.