Dear EarthTalk

My husband thinks it's better for the planet to hand-wash dishes in the sink, but it seems to me using the dishwasher is more eco-friendly. Can you settle this debate for us?

Chris B., Bowie, MD

Hands-down, the dishwasher is the way to go, not only from the standpoint of water waste and energy use but also to preserve your own sanity. Who needs to be scrubbing, rinsing and drying dishes all day when an efficient machine can do the work? Modern dishwashers use much less water and energy than their forebears, so you can clean up after your meals and snacks quickly and without guilt just by filling up the dishwasher and hitting the “start” button.

It’s not surprising that many of us still think handwashing is better, given that the dishwashers of yesteryear used 10-15 gallons of water per cycle. But dishwashers sold today in the United States can only use a maximum of five gallons per cycle per the mandate of the U.S. Department of Energy. And to qualify for one of the federal government’s EnergySTAR labels identifying especially efficient appliances, dishwashers must max out their water use at 3.5 gallons per cycle.

Meanwhile, handwashing the same number of dishes, pots, and pans as you can fit in the dishwasher typically “consumes” some 27 gallons of water, according to a study by researchers at Germany’s University of Bonn. (They also found that some people can handwash a load of dishes with as little as 8.7 gallons of water while others use as many as 116 gallons!)

“The average kitchen faucet has a flow rate of 2.2 gallons per minute, meaning that you’d only have two minutes to wash an entire dishwasher’s worth of dishes to match a dishwasher’s water efficiency,” reports Savannah Sher on BobVila.com. “It would be nearly impossible to use less than five gallons of water to hand wash a full load of dishes.”

And if you’re going to use the dishwasher anyway, save yourself even more hot water by skipping the sink pre-rinse and just loading those dirty dishes right into the bottom rack. 

“Scrape big chunks of leftover food into the trash, but pre-rinsing isn’t necessary with modern dishwashers because they have sensors that adjust the wash cycle based on how dirty the dishes are,” says Consumer Reports’ Perry Santanachote. In fact, unnecessary pre-rinsing can waste about 6,000 gallons of water per household per year.

These efficiency gains only apply to running your dishwasher when it’s full. Rather than running the dishwasher with a half-load, wait until it fills up before hitting start. (Some units have a “rinse and hold” feature that pre-rinses what’s in there so it’s easier to clean when it does fill up later.) Of course, some items—cutting boards, silver flatware, cast iron cookware, non-stick pans—will still require handwashing, but you can always try to minimize your use of them accordingly.

CONTACTS

• A European Comparison of Cleaning Dishes by Hand, https://www.tempurl4.uni-bonn.de/forschung/haushaltstechnik/publikationen/eedal-manualdishwashing-ht1
• Dishwasher vs. Hand Washing: When to Use Each Cleaning Method, https://www.bobvila.com/articles/dishwasher-vs-hand-washing/
• 9 Tricks That Save Tons of Water, https://www.nrdc.org/stories/9-tricks-save-tons-water.