Is it greener to load a dishwasher or hand wash?

When you’re trying to reduce household energy and water use, what are the greenest ways to tackle the daily task of dishwashing?

A new study shows that it is actually best to use an energy-efficient dishwasher, but there is a hand-wash technique that can be resource efficient. The U.S. Department of Energy estimates a typical household washes 215 loads annually. However, even though 80 percent of households in the U.S. own a machine dishwasher, 20 percent use the appliance less than once a week and substitute with manual washing.

A study by the Environmental Research Communications conducted by independent researchers at the University of Michigan found that in most cases, Energy Star dishwashers were more efficient than manual washing. However, to get the best energy and water use results, two steps needed to be eliminated – the pre-rinse and heat-drying cycles. Cutting the pre-rinsing cycle saved 3 percent in the appliance’s greenhouse gas emissions and eliminating the heat drying cycle reduced emissions by an additional 11 percent.

According to the study, manual washing where you leave the hot water running as you clean the dishes produced 5,620 kilograms of greenhouse gases over a 10-year period of washing 32 place settings per week. In comparison, a dishwasher emitted 2,090 kilograms of emissions over the same period with the same loads.

When comparing water use, the difference between manual and machine options was even larger. Over a 10-year period, the average hand washers used 34,200 gallons of water compared to a dishwasher’s 16,300 gallons. When used without pre-rinse and heat-dry cycles, a dishwasher emits 63 percent fewer emissions in its entire lifecycle — including manufacturing and disposal — than a typical sink.

However, there are ways that hand washing can be an energy- and water-efficient option. Using a two-basin sink, the study suggests filling one with hot, soapy water and the other with cool water. Soak and scrub dishes in the hot water and rinse in the cool water. Then let them air dry. According to the study, the two-basin sink method only produces 1,610 kilograms of emissions over 10 years. Adopting this technique leads to a 249-percent reduction in emissions for people who wash dishes manually. So, when strictly followed, it is actually slightly lower than the 1,960 kilograms of emissions a dishwasher produces when it’s being used without pre-rinsing and heat drying.

For more information, find the study at Environmental Research Communications.

Photo: Torbakhopper / CC