I looked at the study and have some concerns about applying it's conclusions. Here is a quote from the abstract.
"The main results are that the washing of smaller amounts of dishes by no means reduces the specific consumption of resources and that the washing of pots and pans is a significant contribution to the consumption of resources. In a comparison with the washing of the same load in a dishwasher, electric dishwashers have a clear advantage over manual dishwashing both in terms of cleaning performance and in terms of the amount of water used. Demonstrating surprisingly good levels of repeatability by the individual test persons, the tests also allowed comparisons "
As it says, it is really about how much dishes you clean and found that cleaning more in one go is more efficient whether by hand or in a machine. This makes sense.
Here is a quote from the body of the report, pg 5
"With regard to energy consumption (Fig. 8), the tendencies are similar, but the difference between manual and automatic dishwashing is not as pronounced. However, the kind of energy used and the corresponding energy losses for both processes will be of a different nature (electricity for automatic dishwashers and usually gas or oil for manual dishwashing) so that comparisons depend on many other factors."
This is relevant to my earlier point about how you heat your water. Direct heating of water via gas or oil rather than through grid supplied electricity is usually more efficient due to losses at power plants and in transmission. Clearly the hands down winner would be solar heated water. The study never looks at the embodied energy of the machine or the energy losses accrued at the end of it's functional life. Another issue to consider is, this is a German study using German machines. They are likely to be of higher quality and of higher efficiency than what is available elsewhere.
I still believe that even if you live in the city you can do better than to purchase an appliance with all it's embodied energy and end of life issues to do a job that can be done by hand with renewable resources. I've lived in the heart of urban Sheffield England until very recently and managed to wash up on occasions using biomass heated rainwater. If I had stayed in that house I would have incorporated systems into the house that would have enabled me to do it all the time. The next time I settle, it will be in a somewhat less dense urban area, I will indeed be setting up systems that increase my resilience and decrease my footprint. It is not that difficult. For the $300-600 dollars or so a quality dishwasher would cost I can set up a homemade solar batch heater from recycled parts, and a water butt, and still have some left over to replumb my sink to divert the gray water into a planter.
Written in February 2009