Which saves more, washing dishes yourself or letting the dishwasher do the work?

Energy saving dishwashers can wash your dishes using less water and energy than if you were to clean them yourself. That's what efficiency experts claim. But is it really the truth?

I used to be skeptical. I can wash the dinner dishes by hand using barely four liters of water, while ENERGY STAR dishwashers use around 4 gallons to a full load, as well as all that electricity to heat the water and slosh it around.

In this article I will share my techniques for washing dishes by hand using as little water and energy as possible. But remember that, for most people, ENERGY STAR dishwashers are a more efficient choice than hand-cleaning, as long as you use the dishwasher appropriately.

If you watch a typical North American clean dishes by hand, it's not hard to see why an efficient dishwasher wins over hand washing almost every time. Some people let the water run continuously as they clean; some fill the sink with hot water and then run cold water in the second sink to rinse; some keep squeezing dish soap into a scrub brush. When you add up all the energy that is required for warming the water, manufacturing the 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 guess.

When people think about a dishwasher, they tend to think of the electricity that pumps water around inside the dishwasher. They imagine that they can save all that energy if they wash dishes themselves. In fact, pumping and draining 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 proper.

You might think that hand-cleaning would at a minimum save you the remaining 20% of the energy used by the dishwasher. But because people typically use much more water than modern efficient dishwashers, the fact is that there is more energy use in hand-cleaning than when using a good quality dishwasher. (Older dishwashers use up to twice as much water as the most recent dishwashers, so it is possible to do better by hand than that old avocado-colored 1970's model!)

Energy efficient dishwashers can clean dishes with a tiny volume of water by doing two things you cannot match when washing by hand: Heating the water to 140F - too hot for your hands - because hot water is better at getting grease and food waste from dishes; and circulating the water at high pressure, which blasts waste off plates and cutlery more effectively than you can hand-scrub it, consuming a tiny amount of water to do so.

Where modern efficient dishwashers are less efficient is where people undermine the energy efficiency features of the dishwasher, by pre-rinsing, keeping their hot water tank temperature too high, choosing too long a cycle, making excessive use of the rinse-and-hold or heated-dry features, running partial loads, and using too much detergent.

You actually can do better than a dishwasher in terms of energy consumption. Whether it's worth your while 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 at most 1.54 kilowatt hours (kwh) of electricity (including all the energy for mechanical and heat). At a typical cost of $0.10 per kwh, and assuming you clean the dishes by hand using cold water, the most you stand to save is around 15 cents per load.

And this is for a full dishwasher load - which is supposed to accommodate 6-8 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 might save around a cent for every five items if you wash by hand and use cold water.

Let's suppose that you want to clean dishes by hand. I rather enjoy washing dishes; it's good contemplation time, plus it leaves my hands soft and clean! How can you wash dishes by hand most efficiently? 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 residue. That way, when it's time to wash, you won't need as much water.

Go easy on the tap. Turn it on for a few seconds at a time, only when you really need water.

Use a faucet aerator. You can rinse dishes effectively while saving water using an aerator, which injects air bubbles into the water.

Use cold water. Where I live in the tropics, no one washes dishes in hot water, although of course the cold water comes out at a balmy 70F. But you can, at a minimum, wash in lukewarm rather than hot.

Start washing with a hand's depth of warm water in the sink. Wash dishes in that, and rinse in a second sink using cold water. Or stack the dishes after cleaning, and then rinse them all in cold when you're done the wash.

As your mom may have taught you, begin by washing the cleanest dishes - glasses, cups, cutlery, plates, and finally pots and pans.

Using these techniques I can clean dishes from a four person meal in about three liters of hot water. But why would I want to do this? And how many of us can really outperform the efficiency of a well-built, energy saving dishwasher?

If you think you can outperform a new dishwasher, here's convincing research that modern efficient dishwashers not only clean dishes with less energy, water and detergent than human subjects, but also get the dishes cleaner.

A German study asked 113 subjects to clean a dozen dinner place settings of dirty dishes. Each volunteer was left alone in a kitchen and observed on video; energy, water and detergent consumption were measured. The dishes were then inspected for residue using an international cleanliness standard. The same dishwashing setup was tried with energy efficient dishwashers.

The ENERGY STAR dishwashers consumed 15 liters of water and 1-2 kwh of energy to clean 12 place settings, while only two of the over 100 subjects used less than 20 liters of hot water. (Over a third of the human subjects consumed over 100 liters of water each!). However, 70 of those tested did manage to use 2 kwh or less of energy - including 27 who used 1 kwh or less.

The way I read the results of this study, it is possible to match the energy performance of energy saving dishwashers, or even be slightly more energy efficient. But the 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 required only 15 minutes of human work for loading, starting, and unloading. Considering that the US EPA/DOE rates dishwasher efficiency based on 215 loads of dishes per year, a typical hand washer would be adding about 89 hours of effort to their year. That's more than two weeks of 9-to-5 work out of your life!

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