Dishwasher v. Handwashing

Court is now in session!

I have long wondered about this question, but not until today (home sick) have I bothered to look it up. As I'm sure someone (ahem!) would point out in the comments if I did not do so myself, I really detest washing dishes by hand. It's not the action of it, I think it's the frequency with which it must be done. So I admit my bias, but I think you will find the evidence I present here impartial and of the most rigorous scientific standards.

The first place that Goggle sent me was to this TreeHugger.com post on the issue [worth reading for the comments - strong feelings by some there that their dishwashing techniques are powerfully superior to the test conditions]. In short, this summary of a German research report states that

The Bonn study proves that the dishwasher uses only half the energy and one-sixth of the water, less soap too. Even the most sparing and careful washers could not beat the modern dishwasher. The study also rated the cleanliness achieved, again in favor of the washing machine (sorry grandma). There have been studies before, but this is one of the few that stands (wo)man against machine and it sets itself apart by including a thorough analysis of the effect of half-loads and the whole demand range from your cake plate to the grimiest pots.

It links to The University of Bonn's Ag School "Household Technology" Research group. Here is their quite entertaining list of research projects, [for example, Uncertanty of measurement of tumble dryers.]

However, we are after the final word on the dishwashing question. It's actually a bit difficult to find the report the TreeHugger site references, since there has been quite a few obscure dishwashing-related research papers written here. However, I'm pretty sure this is the one in question (pdf file): Washing-up Behaviour and Techniques in Europe.  As the abstract states <SPOILER ALERT>:

In the discourse on global warming and other man-made environmental defects, the energy consumption of household appliances is under close scrutiny. Dishwashers, however, are used to substitute or supplement manual dish-washing, so that the question arises about the environmental effects not only of automatic but also of manual dish-washing. To investigate this question, a test was performed covering seven European countries/regions for which the consumption and performance of manual dish-washing was compared with the equivalent data for dish-washing machines, following standardised conditions (EN 50242). As result out of the investigation of 113 persons it is found that the average consumption to clean 12 place settings of dishes was measured to 103 litres of water, 2,5 kWh of energy and 79 minutes time. When these data are compared with values of a new A/A/A dishwashing machine (best machines according to European Energy Labelling scheme taking about 15 litre of water and 1,05 kWh of energy for a full load), possible savings get evident. For a full load this results in 88l water per cycle or about 32,000 litre a year saved when the dishwasher is used once per day fully loaded.

I must state that the report is a literary masterpiece. It combines a very rigorous case-study approach with a fine statistical analysis. The case studies are not to be missed. Who would have thought that a page long description of how a specific person washes dishes would be so interesting? (And I'm talking micro detail here)  However, the more of these you read, the better it gets. The differences in style and approach to hand dishwashing in this study is intense. At the end of each, you can read exactly how much water, energy (heat for the hot water), time, and soap was consumed by each technique. Some techniques used 20x more water than others!

The novel's report's coup de grace, however, comes when, on page 9, the author slips into the summary table a comparison of use of a dishwasher to all the hand techniques used.  Guess what? The dishwasher uses less water, less to about the same energy, takes less (human) time, and produces cleaner dishes than the handwashing techniques. The biggest difference was in the water-usage area -- only the most miserly handwashers even came close to the dishwasher in water consumption...however, their dishes did not get as clean as their techniques necessitated re-use of dishwater. [they measured cleanliness as well]

Also fascinating was to find out that there is an international standard for the creation of dirty dishes for use in dishwashing-related research. I shit you not.

Um, I guess it should be noted, in all fairness, that the dishwasher comparison was for newer (and presumably European) dishwashers. Not sure how US dishwashers stack up for energy and water use that way.

I'm sure there is research that proves the opposite. Handwashers, fire away!

Comments

[jessamyn]

I actually had a houseguest here a few days ago who did not know how to do dishes by hand. This place has a dishwasher but more often than not, I'm washing dishes by hand. If I put them in the dishwasher, I only make about a dishwasher-load a week and by the time I add the last dishes, the first ones are... grotty. As it is, I wash yesterday's dishes while I'm making today's coffee and they get done same day. May use more energy, definitely uses fewer dishes. Maybe if you entertain more?