After reading Why dishwashers are greener than washing by hand, a number of commenters complained that it didn't take into account “the cost of the materials and manufacturing and shipping and fuel on both sides (building and trashing/recycling/whatever happens to it when its trash)”. The commenters make a very good point. That’s what’s known as a life-cycle assessment (LCA), and it is an important issue that's often overlooked.

The embodied energy and the environmental cost of mining minerals, refining them into metals, making plastics and manufacturing the product, then shipping it across the ocean and trucking it to your home does add up. The longevity of the device matters too, and appliances are not lasting as long as they used to. 

The trouble is, they don’t print this stuff on energy labels yet. There's an impetus to develop what are called Environmental Product Declarations (EPDs) for product categories where they look at all the factors, and appliance manufacturers are putting it to use. And while this material may sound a little dry, it's important. Peter Arsenault wrote in an article on Life-Cycle Assessments for Appliances:

LCA results can also be used to assess the environmental footprint of a product over time and to support marketing claims for products. It is important to remember that LCA is a complex modeling tool that has to rely on the best possible data available to provide a good estimate of impacts. Nonetheless, becoming aware of where the biggest environmental impacts in a product’s life cycle exist gives manufacturers clear direction for making important changes to reduce those impacts.
lifecycle of an appliance, from cradle to grave

A full lifecycle analysis looks at everything, from cradle to grave. (Photo: Whirlpool)

The appliance manufacturers have developed LCA standards for washing machines and refrigerators that determine a total score that includes the materials, manufacturing and end of life disposal as well as the energy and water use. Arsenault mentions dishwashers as well:

Water usage has been a similarly strong focus for appliances like dishwashers and clothes washers that need water to operate. LCA studies have found, for example, that many dishwashers have become so efficient in their use of water that it is now much more favorable to the environment to wash dishes using a dishwasher compared to hand washing. By reducing the water consumption overall, water as a resource is depleted less and the environmental impact of processing and treating that water is less. Water consuming appliances like dishwashers have increased in efficiency to the point where they use less water than washing dishes by hand.
I spent some time looking for these LCAs and have only found this graph in one general article that alludes to them:

Life Cycle analysis energy results for several appliances

Look how much use dominates this graphic. (Photo: Appliance Remanufacturing and Life Cycle Energy and Economic Savings)

If you do a quick back-of-the envelope analysis, it becomes clear that over the 10-year life of a dishwasher, it uses a lot of water and energy that quickly overwhelms the embodied energy. Seriously ballpark assumptions using data from Low-Tech Magazine:

energy to make dishwasher

This is a wild approximation, but let's assume it's close. It takes 340 kWh of energy to make the dishwasher, yet it takes 295 kWh per year to run an Energy Star rated unit (1.37 kWh per use). It takes a little over a year, and 248 uses of the dishwasher to use more energy than it took to make it.

Meanwhile, according to a 2011 Bonn University study, the average hand washing American uses 140 liters (40 U.S. gallons!) per wash, with an energy consumption of 3.5 kWh. An Energy Star rated dishwasher uses 4 gallons. 

Here's the energy use from the same study. Americans use more energy hand washing dishes in just 10 washes than it takes to make the dishwasher. You would have to wash like a frugal Australian (9 gallons of water, 1.2 kWh) to beat it in energy, and even they use more than twice as much water.

There are other factors to consider; the dishwasher costs about $600, so there is an economic cost of $ 0.27 for each use. There is an environmental cost if the dishwasher detergent has phosphates in it (they are not banned everywhere yet). But clearly, even taking the life cycle analysis approach on an appliance that uses water and electricity every day, the operating energy and water consumption overwhelms the manufacturing, and unless you're incredibly careful with your water use, the dishwasher appears to win. 

It goes against intuition and all our preaching about the benefits of low-tech simple living, but that's what the numbers say — and I am sticking to it. 

Related on MNN and TreeHugger:

Lloyd Alter ( @lloydalter ) writes about smart (and dumb) tech with a side of design and a dash of boomer angst.

Life Cycle Analysis doesn't budge outcome of the great dishwasher debate
Even if you take the energy and water it takes to build a dishwasher into account, it still beats washing by hand.