Comparing the efficiency of hand-washing versus using an automatic dishwasher is a difficult, if not fairly impossible task, since it all boils down to user habits. A water-miser who uses one basin for lukewarm wash-water and another basin filled with cold for rinsing may come closest to beating or even exceeding a dishwasher’s energy and water use. But most studies and sites conclude that if you run your dishwasher when it’s full, a dishwasher is likely to be more efficient.
At the University of Bonn in Germany, one study measured the dish-washing habits of 113 people from seven different countries, and found that water use from hand-washing dishes varied considerably. The study grouped individuals as “superwashers” (the people who preclean, soap clean, and rinse); “economizers,” who put soap on a sponge, using as little water as possible; and “carefree” washers, who were profligate water and soap users.
In the study, each person washed 12 place settings. On average, hand-washing used 27 gallons of water and 2.5 kWh of water-heating energy. The automatic dishwasher used approximately 4 gallons of water, and consumed 1 to 2 kWh of total energy, which agrees with U.S. DOE statistics on Energy Star-rated dishwashers’ water and energy usage.
Whatever method you use—manual or automatic—here are some tips for saving water and energy when it comes to dishwashing:
- Remove large food scraps before you wash.
- Don’t delay, if you’re hand-washing.
- Skip pre-rinsing the dishes under running tap water, whether washing them by hand or in a machine.
- Manual dishwashing is best in two sinks: one with hot water and detergent; the other with cold water for rinse.
- Use the amount of detergent recommended by the manufacturer.
- Run your dishwasher with full loads only.
- Use your dishwasher’s air-dry feature instead of its heat-dry cycle.
- Use a dishwasher that’s fairly new—made in the past few years. Some newer units also have “booster heaters” that heat the water on demand versus from your water heater, helping save energy.