Avoid prewashing. Prewashing dishes―once necessary to yield clean items from the dishwasher―wastes time and water. As a result of new dishwasher technology, you simply scrape dishes before loading. "Rinsing dishes before loading them in the dishwasher uses up to 20 gallons of water. Washing by hand is worse, requiring about 27 gallons to do an equivalent full load," says Richard Karney, ENERGY STAR program manager with the U.S. Department of Energy. "Compare that to the normal cycle on new ENERGY STAR-qualified dishwashers, which use only four gallons of water."
Run a full load. Because most dishwashers use the same amount of energy and water regardless of how full they are, wash only full loads (or use the half-load feature when needed, if available). If dishes need to sit overnight because you don't have a full load, run the rinse-only feature, which uses about a gallon of water. When you have overflow dishes or lots of pots, such as after parties or holiday meals, run a second load; you'll still use less water than washing by hand.
Use a rinse agent. Rinse agents also help reduce energy usage. "They affect the surface tension of water so it flows more easily off dishes," Topping says. "Water sheets off instead of beading up so you can choose to drip-dry instead of using a heated dry cycle, which uses more energy." Because remaining water is spread thinly on glasses instead of left in droplets that shrink, dry, and leave behind residual minerals, spotting may also be reduced.