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the green lantern: Illuminating answers to environmental questions.

Is a Dishwasher a Green Machine?The soapy sponge may not be worth your time.

By Brendan I. Koerner
Updated Tuesday, April 22, 2008, at 7:56 AM ET
Dishwashers can be more eco-friendly than hand-washing. Click image to expand.

I've always taken great eco-pride in the fact that I hand-wash all my plates and glasses, thereby eliminating the need for an electricity-slurping dishwasher. But my sister says that I've got it all wrong—using a machine, she insists, is more environmentally sound than doing the chore yourself. Have my good intentions been for naught?

To properly answer this question, the Lantern would have to spend a few nights in your kitchen, armed with a stopwatch and various measuring implements. That's because much depends on your specific hand-washing technique. Do you fill the basin, or do you let the faucet run? Do you scrape off crusty particles or hope that the jet of water does the trick? Are you cool with dishes piling up over the course of the day, or are you a stickler for washing them right away? If you adhere to the most efficient hand-washing regimen imaginable, you can probably beat a machine. But your margin of victory may be disappointingly slight, and hardly enough to justify all the extra time.

Your intuitive preference for hand-washing may harken back to your childhood, when dishwashers were gluttons for energy and water. But much has changed in recent years—between 1993 and 2003, for example, the average machine became 27 percent more energy efficient and 30 percent more water efficient. Today's most advanced machines use just a single kilowatt hour of electricity per load, and as little as 3.18 gallons of water. (Similarly impressive improvements in washing-machine efficiency have altered the environmental debate over diapers.)

These efficiency improvements were highlighted in a much-discussed study (PDF) from the University of Bonn, published four years ago. More than 100 Europeans were observed cleaning a dozen full place-settings by hand. The German researchers found that the average hand-washer is quite the wastrel, using 27.2 gallons of water, which requires 2.5 kWh of electricity to heat. (The most careless hand-washers were Spanish and Portuguese, while the most economical were German.) An ultra-efficient machine, by contrast, used only between 3.96 and 5.81 gallons of water, and between 1 and 2 kWh of electricity.

Advantage, technology. But if you read the German study carefully, you'll see that the best hand-washers came close to matching the machine's performance. These paragons of efficiency employed a few key tricks, among them using two-basin sinks and filling one basin with hot, soapy water and the other with cold water for rinsing. They also scraped off crusty food particles, rather than wash them away with running water. Such clever hand-washers were able to keep their daily water usage below eight gallons, well within spitting distance of the machine. And their electricity usage was just 1 kWh per day.

Those skilled hand-washers look even better when you consider the environmental costs of manufacturing, transporting, and (eventually) disposing of a machine, none of which were factored into the German study. Nor did the researchers consider the fact that dishwashing detergents often contain phosphates, which can cause ecologically harmful algal blooms in waterways. And gas-powered water heaters, which are common in the United States, are more efficient than the electrical heaters considered by the Germans.

It's also worth noting that not all dishwasher owners use their machines in the most efficient manner possible. To really green up your automatic dishwashing, you should always use the air-drying function, avoid the profligate "rinse hold" setting, wash only full loads, and install the machine far away from your refrigerator. (The dishwasher's heat will force your fridge to work harder and thus negate your supposed energy savings.)

Despite all of these complicating factors, the German researches have stood by their conclusions, most recently in a 2007 follow-up (PDF) to their initial report. And their pro-machines sentiment is seconded in a widely circulated pamphlet (PDF), which estimates that using an EnergyStar dishwasher will save you $35 per year on water and energy costs.

But the Lantern is skeptical of that assertion, since it relies on the University of Bonn data for hand-washing, and on manufacturer-supplied estimates of machine performance. The authors of a British study (PDF) funded by the United Kingdom's sustainable products agency comes to a more measured conclusion: "Claims that dishwashers are more energy efficient than hand washing are sometimes made and have no foundation."

That sounds about right to the Lantern, especially if you factor in a life-cycle analysis of a steel dishwasher manufactured in China (which typically last between nine and 11 years). If you're truly dedicated to hand-washing the right way, you'll usually come out ahead of the average machine.

But do you have that level of dedication? At the end of the day, there won't be much of an environmental difference between an ultra-efficient hand-washer and an ultra-efficient machine, as long as the machine is used wisely. The difference in time consumption, however, can be enormous—a fact that the Lantern, whose Lilliputian apartment lacks a dishwasher, knows all too well. And when you're working long hours and taking care of a family, time is often the most precious commodity.

So if you're content to spend dozens of minutes per day on hand-washing, making sure to follow the environmentally correct protocol each and every time, more power to you. But if you'd rather spend that time on something more rewarding yet don't want to suffer pangs of enviro-guilt, you can switch to an EnergyStar machine with the Lantern's blessing. Just promise that you'll scrape your dishes instead of pre-rinsing, use the shortest wash cycles possible, and buy phosphate-free detergents—or, if you're handy with a blender, make your own.

Is there an environmental quandary that's been keeping you up at night? Send it to , and check this space every Tuesday.

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Brendan I. Koerner is a contributing editor at Wired and a columnist for Gizmodo. His first book, Now the Hell Will Start, will be published by Penguin Press in May 2008.
Photograph of dishwasher courtesy Getty Creative Image.
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