Nobody likes doing dishes, but wouldn’t it take a load off of our shoulders if we knew what the most environmentally responsible way to do them was? Is it in the sink with your hands, or in the dishwasher?

I’ve always heard conflicting advice on which option was greener; add to that that there’s more than one way to manually wash your dishes and that there are more dishwasher models than colours in the rainbow. It gets very complicated very quickly.

Here at Ecoblogist, we dusted off our Grade 9 math textbooks, hunted around for some statistics on energy use and came up with an answer that, while not definitive, at least points you in the right general direction.We took into account both water use, and the energy that was required to run the dishwasher and to heat the water by 30 degrees Celsius in your hot water heater. We even counted the energy that your utility spends treating and pumping the water to your home and then pumping and treating the…um…wastewater at the other end of the line.

photo by kristin slota

Method 1: Running the Sink for 10 minutes on hot.

Water use: 83 L/time

Energy use: 140.5 kWh/year

This is a popular way to wash dishes if you don’t have a dishwasher. Simply turn the faucet to hot on full blast and run the water for 10 minutes while you soap up your dishes and then rinse them under a constantly running stream.

Washing your dishes this way is pretty wasteful: it uses 83 L of water, which is enough to fill your bathtub halfway to the top (or about what you would need to use to take a bath). The energy use is relatively modest, however, at 140.5 kWh/year – most of which (105 kWh) is used to heat that vast quantity of water. Not surprisingly, 35 kWh a year is spent by your public utility to pump and treat the water and wastewater from running your faucet on high for ten minutes every day.

Method 2: Fill both sides of a two-basin sink; fill one side with dishsoap to wash, use the other side to rinse.

Water use: 29.5 L/time

Energy use: 49.9 kWh/year

I was taught this method in Home Economics class in Grade 8, but I always questioned whether it was the cleanest way to wash your dishes. Nevertheless, it is the most environmentally friendly, since it only uses 49.9 kWh of electricity/year – mostly to heat the relatively small amount of water you use each time. It doesn’t, however, save as much water as a dishwasher (see Methods 3 and 4). This was the hardest of the 4 methods to calculate, since people very often will drain the sink and refill both sides when the water in either basin becomes too gross. Does that mean that people will use twice as much water and energy as we originally thought? It’s hard to say, since people all have their own preferences.

Method 3: Using a Dishwasher

Water use: 23 L/time

Energy use: 784 kWh/year

By “dishwasher”, we’re talking about a standard, non-energy efficient regular model. Even old clunkers use less water than doing the dishes by hand, but they do use tremendous amounts of energy. Not accounting for heating the water (which always uses a majority of the energy), running a dishwasher still eats up 150 kWh a year, which is more than what it takes to treat and heat the water used when you run the sink for 10 minutes every day (Method 1). You can cut down on your energy consumption somewhat by turning off the “Heat Dry” option. Why not let time and air drying take care of removing those pesky water droplets for you? You’ll also avoid getting doused with a blast of hot, moist air when you finally open the dishwasher door.

photo by kristin slota

Method 4: Using an Energy Star Dishwasher

Water use: 15 L/time

Energy use: 308 kWh/year

Energy Star dishwashers purportedly use 61% less energy than regular dishwashers, and about 8 L less water, to boot, making this method the most water efficient way of doing your dishes. They’re still energy hogs compared to washing your dishes by hand, but there’s an upside to them: I have an Energy Star dishwasher at home, and I find that my girlfriend and I only need to wash the dishes every other day. We don’t use too many dishes and we find that when they’re squirreled away in the dishwasher, they’re out of sight and out of mind. Back when I was single, however, I didn’t have a dishwasher at all and I found that having a pile of dirty dishes climb ever higher in the sink was not exactly a sight for sore eyes. As a result, I was constantly washing my dishes and found myself standing in front of the sink at least once, or sometimes even twice a day. With this in mind, I am probably saving energy by running the dishwasher half as often as I would if I washed by hand. Often it’s our dishwashing habits that determine our environmental footprint.

Final verdict?

If you consider energy use more important than water use (I do, because energy is used to treat and pump the water we use, anyway) washing by hand is more environmentally friendly than washing using the machine. However, psychological effects can be just as important in our environmental impact. Some people will refill the sink two or even three times to make sure the water is crystal clear while people like me find that they use the dishwasher half as often as they would if they washed by hand because of the psychological impact of constantly staring at dirty dishes in the sink. It’s important to be aware of these effects when you consider which dishwashing method will have the least environmental impact for your lifestyle.

by guest blogger Leonard Machler

I’m often asked why we should bother saving water in a country like Canada, which is home to ¼ of the world’s fresh water.  One good reason – beyond the fact that many of us, particularly in the Prairies and the interior of British Columbia, live in drought-prone areas – is that it takes a lot of energy to treat drinking water, distribute it through the system and then treat it again as wastewater.

As much as 3% of total energy use in North America is spent on water and wastewater treatment, and more than half of all water use in Canada is residential…

The average Canadian uses 335 L of water every day.  Just flushing a low-flow toilet will use enough electricity to power a 60 watt light bulb for 6 minutes.  The amount of energy required to supply every Canadian household with water is enough to power over 370,000 homes – or every house in Saskatchewan!

Unfortunately, the energy costs of using water are not accounted for both in our everyday thinking as well as on environmental calculators, including our own EcoAction Calculator.  We’ve highlighted the importance of saving water on our calculator with such activities as Save Every Drop in the Sink, Damming your Toilet Tanks and Installing Faucet Aerators but, here at ecoblogist, we will start a new series that highlights the true environmental savings of reducing your water use.

NEXT: Dishing the dirt on dishwashers…

Leonard Machler is doing his Masters degree in Sustainability at Arizona State University.  Living in the arid Southwest reminds him of the importance of water and this has inspired him to write a blog series on water savings activities for Ecoblogist. When he’s not baking in the desert, he divides his time between Toronto and Peterborough, Ontario.