Perhaps it has become a friendly debate between generations: Grandma spent her youth helping her mother wash and dry the dinner dishes, while her own grandchild has never lived in a house without a dishwasher. So which method uses more water? Which is more ecologically smart?
Washing By Hand
How much water you use to wash dishes in the sink will vary for a number of reasons, such as how dirty and greasy the dishes are, the rate at which water pours from your faucet, and how many dishes you are washing. The only way to compare hand-washing to machine-washing is to wash the same amount of (similarly dirty) dishes that would comfortably fill a dishwasher for one overnight load.
Measured by a flow meter attached to the kitchen faucet, experiments have shown that washing a comfortable dishwasher load by hand can use up to twelve gallons of water.
Filling Up The Dishwasher
Dishwashers vary in the amount of water they use. Newer rules call for bringing down the per-cycle limit to 3.1 gallons, which would save billions of gallons of water a year. Some Energy Star brands currently use only four gallons per cycle. To make this fight fair, let’s assume the dishwasher in use is a standard, non-Energy-Star brand that uses six full gallons per cycle.
Already, washing dishes in a dishwasher saves 50% more water than washing dishes by hand.
If you’re surprised by the results, consider how dishwashers work. Generally, fresh water is only drawn into the tub at the beginning of the cycle and then again at the end, to rinse away the last of the soap and debris. In between, water is reheated, filtered, and recycled to keep the scrub cycle going.
Of course, these calculations change if you rinse all your dishes before putting them into the dishwasher or run less-than-full loads. But, if you follow the rules, the dishwasher beats out hand-washing not just in time but also in money.