A dishwasher uses between 5 and 15 gallons of water per load. The exact amount depends on the age of the dishwasher.
Older dishwashers tend to use more water per load as they are not as energy efficient as newer models. When using an older dishwasher, a family of four can use 1,800 gallons of water per year. The average family washes around 150 loads of dishes in a dishwasher annually. By using a newer, energy efficient machine, a family of four can save between 500 and 1,000 gallons of water yearly. The exact amounts varies depending on the amount of usage.