Cleaning Up After Dinner: Save Time And Energy, Hand Washing Dishes Wastes Energy!

Energy efficient dishwashers can clean your dishes using less water and electricity than if you were to clean them yourself. That's what efficiency experts claim. But is this really true?

I didn't think so until recently. I can clean the dinner dishes myself using about four liters of water, while energy saving dishwashers use around 4 gallons to a full load, plus all that electricity to heat the water and pump it around.

I would like to share my techniques for cleaning dishes by hand using as little water and energy as possible. But remember that, for most people, energy saving dishwashers are a more efficient option than hand-washing, as long as you use the dishwasher properly.

If you observe a typical North American clean dishes by hand, it's easy to see why an efficient dishwasher beats washing by hand just about every time. Some people let the tap run continuously as they wash; some fill the sink with warm water and run cold water in the second sink for rinsing; some are constantly pumping dish soap into a sponge. When you add up all the energy that went into warming the water, manufacturing the dish soap, and even the energy for purifying and pumping the water to your home, it can wind up being a lot more energy than you would imagine.

When people think about a dishwasher, they usually think of the electricity used to pump water around inside. They might think that they'll save all that energy if they clean dishes themselves. In fact, pumping the water uses less energy than heating the water - only 20% of the total, compared to 80% for heating when you consider the heating that takes place in your hot water tank and in the dishwasher itself.

You might think that hand-cleaning dishes would at least save you the remaining 20% of the energy used for pumping. But because people typically use much more water than ENERGY STAR dishwashers, the end result is more energy use in hand-washing than when using a good quality dishwasher. (Older models use up to twice as much hot water as newer dishwashers, so you might outperform that old goldenrod-colored 1970's model!)

Efficient dishwashers can clean dishes with a very small amount of water by doing two things you cannot do as a hand washer: Heating the water to 140F - because hot water is better at getting grease and food waste off dishes; and pumping the water at high pressure, which blasts food off your dishes more effectively than you can do with a scrub brush, using a very small amount of water to do so.

Where ENERGY STAR dishwashers are not so energy efficient is where people sabotage the energy saving features of the appliance, by pre-rinsing, keeping their hot water tank temperature too high, using too heavy duty a cycle, making excessive use of the rinse-and-hold or heated-dry features, running the unit half empty, and using too much dishwasher detergent.

It is possible to do better than a dishwasher in terms of energy consumption. Whether it's worth the effort is another matter. Consider the fact that energy efficient dishwashers with an ENERGY STAR logo can do a full load for the energy equivalent of less than 1.55 kilowatt hours (kwh) of electricity (that includes both the energy for mechanical and heat). At a typical cost of ten cents per kwh, and assuming you wash the dishes using cold water, the most you would save is about a dollar for every six loads.

And this is for a full dishwasher load - which is supposed to hold 6-8 complete place settings as well as 6 serving pieces. Assuming bread plate, dinner plate, bowl, cup and saucer, knife, fork and spoon, that's about 72 items cleaned, so you'll save about a cent for every five items if you wash by hand and use no energy.

Let's assume that you really do want to clean dishes yourself. I actually like washing dishes; it's a good time for thinking, plus it cleans my fingernails! How can you wash dishes by hand using as little energy as possible? Here are my pointers:

Never drain used water. After you've cleaned a load of dishes by hand, or rinsed vegetables, leave the water for later rinsing. Use this gray water to pre-rinse the dishes to remove most of the grease and other food residues. That way, when the time comes to clean, you won't need as much water.

Go easy on the tap. Run the water for short bursts, only when you really need water.

Use aerators on your kitchen faucet. You can rinse dishes effectively while saving water using an aerator, which injects a stream of air into the water.

Use cold or just lukewarm water. Where I live in Central America, no one washes dishes in hot water, but granted, the cold water tap is a balmy 70F. This just goes to show that you can, at the very least, wash in lukewarm rather than hot.

Start with an inch of warm water. Wash dishes in that, and rinse in a second sink with cold water. Or stack the dishes on the counter after washing, and then rinse them all in cold after you finish the soap wash.

Just like your mom taught you, start by washing the cleanest dishes - glasses, cups, cutlery, plates, leaving the dirty pots and pans for last.

By following these techniques I can wash dishes from a meal for four people in less than a gallon of fresh water. But is it worth all the effort? And how many people can really outperform the efficiency of a well-built, energy saving dishwasher?

If you think you can beat a new dishwasher, here's convincing evidence that modern efficient dishwashers not only clean dishes using less energy, water and detergent than people do, but also get the dishes cleaner.

A study in Germany asked over 100 subjects to clean 12 dinner place settings of dirty dishes. Each volunteer was left alone in a washing area and observed by camera; energy, water and detergent use were tracked. The dishes were then inspected for cleanliness using an international cleanliness standard. The same test was repeated with ENERGY STAR dishwashers.

The efficient dishwashers consumed 15 liters of water and 1-2 kwh of energy to clean 12 place settings, while only two of the 113 hand-washers consumed less than 20 liters of hot water. (Over a third of the hand-washers consumed over 100 liters of water each!). However, 70 of those tested did manage to use no than 2 kwh of energy - including 27 who used 1 kwh or less.

The way I read the results of this study, you can match the efficiency of ENERGY STAR dishwashers, or even be slightly more energy efficient. But the amount of energy saved is so small that it doesn't justify the extra effort. The human hand-washers took at least 40 minutes to do the load, while the energy efficient dishwashers needed only a quarter hour of human work for loading, starting, and unloading the dishes. Considering that the US EPA/DOE rates dishwasher efficiency assuming 215 loads of dishes per year, a typical hand washer would be adding 25 x 215 minutes, or 89 hours of work to their year. That's more than two weeks of 9-to-5 work out of your life!

You are probably better off to save that effort and look at other things you can do to save energy. Just think how efficient your house would be if you devoted an extra 89 hours a year towards weather-stripping, sealing air leaks, and changing light bulbs to more energy saving lights. Or how much more relaxed you'll be by using your dishwasher. You just gained two extra weeks of free time!