You wouldn't think it, but using a dishwasher as opposed to washing dishes by hand actually saves water and energy in the long run. The most efficient modern dishwashers use between 4 and 6 gallons of water per cycle according to Energy Star1. In contrast, the average faucet can run as much as 2.5 gallons per minute2, according to federal plumbing standards.
Assuming 2.5 gallons of water flow from your sink per minute, in 5 minutes of hand dish washing time with the hot water running, you will have used 12.5 gallons of water. That's twice the amount of water used by a modern dishwasher. From an energy perspective, it takes about 6.63 kWh to heat a 40 gallon tank of water using your electric water heater3, so you are actually using more water to wash dishes by hand than you would if you were using the dishwasher. Add to this the need for the water to be hot - using energy from your hot water heater - and you've got quite a bit of waste on your hands.
Using Your Dishwasher for Maximum Efficiency
First, make sure you have an efficient dishwasher.
If your dishwasher is old or out of date, then chances are it's using up too much water and energy. How old is too old? According to Energy Star, any dishwasher made before 1994 is a culprit. Upgrade your appliance if you fall in this category, you could save hundreds of gallons a year. Make sure that the machine is Energy Star certified. This ensures that the dishwasher is an energy efficient one.
Next, reduce the amount of time you spend hand washing dishes. Use the dishwasher whenever possible, and wait to run it until it's full.
Finally, be conscious of how you use your dishwasher. Many dishwashers also have an Eco-Mode setting4, which will limit the temperature and quantity water used for washing dishes. (This setting is best for lightly soiled dishes.) Other units may offer condensation drying systems, which are far more energy efficient than units that use a heating element to dry dishes.