No matter how you wash dishes—whether by hand or with a dishwasher—there are environmental impacts. Both use water and energy, as well as potentially harmful soaps and detergents.

Dishwashing versus hand washing

Who's the biggest waster: dishwashing or handwashing? Americans consume an average of 80 to 100 gallons of water a day.[1] How much goes toward dishwashing depends on how often a load is washed and how much water is used (either via hand-washing or a dishwasher).[2]

Debate continues about which method wastes less water. One study by researchers at the University of Bonn in Germany found that hand-washing dishes uses between five and 86 gallons of water compared to four to five gallons for the average European dishwasher. Americans didn't participate in the study, but statistics show the average US dishwasher uses nine to 12 gallons of water per load (less for energy-efficient models), while hand-washing requires around 20 gallons.[3] With American households running a dishwasher only four or five times a week, on average, that represents a considerable savings over washing by hand, particularly when dishes are hand-washed once or more a day.[4] However, other research shows that hand-washing dishes by filling a dishpan or sink basin and refraining from running additional water consumes half of what a dishwasher uses per load.[5]

The detergent dilemma

Many household cleaning products, including dishwasher detergents and dish liquids, contain toxic chemicals that contribute to unhealthy indoor air pollution. One study of over 4,000 women found that 25 percent of asthma cases among them were the result of exposure to cleaning products.[6] Chemicals in dishwashing liquids and detergents—including petroleum (a non-renewable resource), alkyphenol ethoxylates (suspected hormone disruptors for humans and wildlife), and ethoxylated alcohols that contain the carcinogen 1,4 dioxine—not only harm human health from direct contact, but also contaminate waterways and drinking water when washed down the drain (harming people, wildlife and ecosystems).[7]

In addition, many commercial dishwasher detergents contain phosphates, which prevent those filmy dishwasher spots, but also promote algae blooms in waterways that rob water and aquatic life of oxygen. Phosphates were voluntarily phased out of laundry detergents by manufacturers in the 1990s after states and localities began to limit them. Many states and localities are now beginning to limit phosphates in dishwasher detergents, but they remain in many brands.[8]

Conserving water and energy

There are ways to make both hand-washing and using a dishwasher more water-efficient. In addition to filling a sink or dishpan to wash and rinse by hand, installing low-flow aerators on faucets (which mix air and water) limits water flow to anywhere from 0.5 to two gallons per minute (gpm) compared to the 3.5 to seven gpm released by standard faucets.[9] In one study, installing aerators on faucets resulted in a 13 percent annual cut in water consumption for each household member and a 10.6 percent drop in hot water use per member.[10] Heating water accounts for about 15 percent of a typical home's total energy bill.[11]

An ENERGY STAR dishwasher uses an average of 1,000 fewer gallons per year than standard dishwashers. In addition, ENERGY STAR models use significantly less electricity, mainly by heating water more efficiently. Because water-heating accounts for 80 percent of the energy used by the average dishwasher, ENERGY STAR brands can save $25-$35 a year.[12]

Dishwashers with built-in hot water boosters bring additional savings by raising the water temperature inside the dishwasher to 140 degrees Fahrenheit (recommended for optimal cleaning). This allows the main household water heater to be turned down to 120 degrees Fahrenheit or less. For every 10 degrees a water heater's thermostat is lowered, the water-heating bill drops by up to 13 percent.[12]

Further water and energy savings come from running a dishwasher only when it’s full, skipping the heat-drying cycle and not pre-rinsing dishes before loading them. For instance, running a dishwasher fully loaded can save up to 400 gallons of water per month.[13] Skipping the heat-drying cycle reduces a dishwasher’s energy use by 15 percent to 50 percent, saving up to $25 a year.[14] Forgoing the pre-rinse in the sink can save up to 25 gallons per load.[15]

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