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Musings of an Energy Nerd

All About Dishwashers

Compared to hand washing, an automatic dishwasher saves energy — but do paper plates and cups save even more?

An efficient dishwasher uses less than 2.5 gallons of water and 1 kWh of electricity to wash a full load of dishes. The photo shows the Energy-Star-rated Bosch 800 Plus dishwasher.
Image Credit: Bosch

An automatic dishwasher uses hot water and electricity, so it makes sense to choose an efficient model. But before discussing the question of which dishwasher you should buy, we need to address two questions:

  • Does washing dishes by hand save energy compared to an automatic dishwasher?
  • Does the use of paper plates and paper cups require more or less energy than using china plates and cups?

Hand washing versus automatic dishwashers

The definitive research on the first question was performed in 2004 in Bonn, Germany, by researcher Rainer Stamminger. Stamminger reported his findings in an article for English-speaking readers (“Is a Machine More Efficient Than the Hand?”), published in the May/June 2004 issue of Home Energy magazine.

Stamminger found that a dishwasher uses about half the energy and one-sixth the water used by the average hand-washer. (The appliances used in Stamminger’s study used an average of about 4 gallons of water and about 1 kWh of electricity per load for a standard washing cycle.) Moreover, the automatic dishwasher used less detergent and got the dishes cleaner.

“To rule out possible regional differences in dishwashing techniques, we persuaded 113 people from seven countries in Europe to participate in the dishwashing experiment,” Stamminger wrote in the Home Energy article. “The subject was asked to clean and dry the dishes as he or she would do it at home. … For manual dishwashing, results below 3.5 were regarded as ‘really dirty’ or ‘not acceptable to be placed on a dinner table.’ Clearly, about half of our test subjects did not achieve an acceptable level of cleanliness.”

If you are washing dishes by hand, it’s extremely hard to do a good job with the same amount of hot water used by an automatic dishwasher. “To clean the 12 place settings of dishes, the 113 test subjects used on average…

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  1. mfredericks | | #1

    Low flow faucet aerators
    Thanks Martin, I'm always curious about these studies as most people commonly expect hand washing to be more efficient, and re-usable dishes are always best. Despite the evidence, I'm not likely to give up my coffee mug!

    We have a really old Kenmore dishwasher and I'd like to compare it's water/energy consumption to my hand washing process which is using very little water after I installed a 1.5 gpm faucet aerator on my kitchen sink and I'm careful to use as little water as possible. With aerators now available with flow ratings as low as 0.5 gpm, (and a mixture of hot/cold water for hand washing rather than all hot) I wonder if hand washing could be more efficient for those homes that have an older dishwasher and could easily add a low flow aerator to the sink for just a few dollars? Did you come across this scenario in your research, Martin?

  2. GBA Editor
    Martin Holladay | | #2

    Response to Mark Fredericks
    To beat a dishwasher, you have to come up with a way to wash and rinse 12 place settings of dishes — 140 individual pieces, including china, glasses, and cutlery — in less than 4 gallons of water. It's just barely possible, but it's hard to do; and if the dishes are soiled heavily, the wash water will look pretty disgusting at the end of the job.

    Having a low-flow aerator is irrelevant, because there is no way you can beat the dishwasher if you leave the faucet running. The only way to have any hope of beating the dishwasher is to wash dishes the way your grandmother did: with two dishpans, one with soapy water for washing and one with clear water for rinsing. This is the way most people wash dishes when they are camping.

  3. Expert Member
    Dana Dorsett | | #3

    Who washes their coffee cup after every fill...
    ... and who refills paper or polystyrene disposables?

    The math gets a little fuzzy when re-considering some of the primary assumptions. The mug next to my monitor may get washed once every 3-5 days, but gets filled 3-4x every day, so you're looking at something on the order of a dozen fills per wash. I doubt I'd refill plastic or paper coffee cups anywhere near as often between disposals.

    FWIW: Gas/propane fired on-demand tankless HW heaters all have an ignition delay, and many will almost NEVER supply a substantial fraction of the hot water to a modern dish washer, or even many clothes-washers that fill in intermittent short-draw bursts, even with fairly short distribution runs to the appliances.

  4. GBA Editor
    Martin Holladay | | #4

    Response to Dana Dorsett
    All of the energy life-cycle analyses of the china vs. paper issue which I quoted assumed that each disposable cup was used only once. However, if you reuse a disposable cup, you get a gold star.

    Concerning your habit of washing your mug only after drinking 10 to 20 cups of coffee: as with any energy calculation, your mileage may vary.

  5. LukeInClimateZone7 | | #5

    Not What Weapons of Mass Destruction-- What would Martin Do?

    Martin, in the midst of this, and previous forums you had on dishwashing techniques, I think it would it would be interesting to take you out of the journalist/blogger role and ask you tell us how you wash your dishes. If I remember correctly you yourself are a handwasher, and I suspect you're a reasonably efficient one.

    As for me-- I violate your first efficiency selection by pre-rinsing my dishes. I find it's easier to pre-rinse than to spend the several minutes it takes each week to unclog my dishwasher's filter and sprayers.
    The extra step that I take which may make the difference in efficiency is that I pre-rinse or (outright wash if I only have a few dishes) into a dishtub which I then take outside to water parts of my landscape. So, I'm able to turn my dishwashing wastewater into an ersatz greywater system. I use that term loosely since I know most plumbing codes aren't liberal enough to consider dishwashing water as greywater.
    This may not literally be the most efficient, since I might be washing dishes twice sometimes, but I think it's still a move in the right direction relative to the average.

  6. GBA Editor
    Martin Holladay | | #6

    Response to Lucas Morton
    I don't have a dishwasher. I live in an off-grid house, and I don't use much electricity.

    I use the two-dishpan method. During the summer, most of the hot water is heated by my two solar thermal collectors; the solar hot water system has a DC pump that is energized by a dedicated PV panel. During the winter, most of the hot water is heated by a stainless-steel coil in my wood stove that circulates water to a tank on the second floor of my house by thermosyphon.

  7. user-831308 | | #7

    Perhaps grandma had it right?
    I am always skeptical when I hear about these dishwasher studies, because so many of them seem to arise from appliance manufactures. However, I really appreciate the thorough analysis made in this particular study. My problem with these tests has always been that they are designed around the dishwahser: fully loaded and at at it's optimal efficiency.
    What I have observed is that people don't always run a full load dishes, because it's been a few days and they are tired of looking at crusty dishes, or they've run out of dishes to use. I'd be very curious how the results would be with a half-load of dishes. I just wonder if people handwashing a more "manageable" number of dishes would affect their water/energy consumption, for better or for worse. Also, throw in some cooking pots and pans as well to the test for some real world comparison. (Can they even fit in the dishwasher?)

    I know in our house (family of five), we only use the dishwasher when we have many people over. Although we have an Energy Star dishwasher, we are not impressed with it's performance whatsoever (a Kitchenaid drawer style). Perhaps we would feel much better if we had something that actually cleaned well.

    I have found that the most efficient way we do dishes at home (or while camping) is to have a pot large enough to let the dishes simply soak in hot water for several minutes, prior to any cleaning. This makes the rest of the cleaning process much easier. And the last time I checked, my drying rack sitting on the counter over the dishwasher uses a lot less energy to dry than the dishwasher (and I can't turn the dishwasher off after it has washed, to air dry.)

  8. GBA Editor
    Martin Holladay | | #8

    Response to Matt Dirksen
    It's possible to wash dishes badly by almost any method. If you have a dishwasher, you can wash dishes badly by using lots of running hot water to pre-rinse the dishes, by always running the appliance when it is only half full, and by insisting on using the electric drying function every time you use the machine.

    If you want to wash dishes badly by hand, all you have do is wash them the way most people do -- with the faucet running continuously.

    Any energy comparison depends on data. The data collected on hand washing methods are, of course, based on a range of behaviors. That said, even the most frugal dishwashers would be hard pressed to wash and rinse 140 items -- that's 12 place settings, or a full Thanksgiving dinner with all the aunts and uncles, and both sets of grandparents -- with 4 gallons of hot water. That's why I would be reluctant to recommend hand washing.

    Everyone thinks they are frugal. Everyone thinks that when they wash dishes, they never waste water. But everyone uses more water than they are willing to report.

  9. jj1 | | #9

    CEE Listing
    Hi Martin: The Consortium for Energy Efficiency maintains a convenient list, updated monthly, of the energy and water use of dishwashers sold in the US: CEE also maintains a list of top performing dishwashers which meet the stringent CEE standards:

    I intend soon to replace my old dishwasher with a new Bosch 180 KWHr p.a. 2.2 gallon per cycle rated model, plumbed to the cold water input pipe. The 20 to 30 minute extra wait noted in the FSEC study should realistically be a zero to 15 minute incremental wait in my case; the new Bosch would be filling mostly with 2.2 gallons of cool/cold water even if plumbed to the hot water pipe, anyway.

  10. user-831308 | | #10

    yes but...
    My point is: not every day is Thanksgiving.

    I would be much more interested in an analysis which was designed around “typical” use, not “optimal” use. What I have witnessed in the world outside of the laboratory is; people are not fully loading their dishwasher most of the time. Why? Because people are more inclined to run the dishwasher daily to not have dirty dishes sitting around, or they are simply afraid to “overfill” the dishwasher for fear that it will fail to clean all the dishes properly. Are these the same people who would let the water run? Perhaps.
    Perhaps it’s around the corner, but I would sure appreciate a dishwasher (like many front load washing machines) which “knows” how many dishes are inside it, and adjusts the water accordingly. I understand that Bosh has a "half load" setting. I'd be curious to see how well that setting works in real-world settings.
    On the handwashing front: I’d sure love a “thing” over my sink which would begin to shame me for using more water than my dishwasher could have used, to clean the same amount dishes in one standing.

  11. Brent_Eubanks | | #11

    sensitivity to boundary conditions
    The article notes that the study says "The results are extremely sensitive to the amount of energy the dishwasher requires for cleaning each cup."

    I want to point out that the converse is true - the results are extremely sensitive to the assumptions about embodied energy as well, especially in the case of the styrofoam cup: The reason it takes over 1000 uses to break even with stryfoam is the very small embodied energy difference between the styro cup (0.20 MJ) and the the energy cost per cup wash (0.19 MJ). If the styro cup estimate was even 5% higher (0.21 MJ), the number of uses for breakeven would be cut in HALF. That's a tiny difference on the styro cup side - it easily could be the difference between shipping the crate of cups from a factory in one location relative to another.

    I don't mean this as a criticism of this study. This sort of work is notoriously hard to get right, and all values need to be read with implicit error bars - that's the nature of the work. But it's worth pointing out when a result (particularly one that extreme) is so very sensitive to the study's assumptions/estimates. That said, the basic takehome is valid - you have to reuse the cup many, many times for it to break even.

  12. user-946029 | | #12

    Catch 22?
    "Based on my reading of the above analyses, I would say that china plates, bowls, and cups win out over paper — but only just barely, and only under certain conditions:"

    So, if those conditions are not met, then paper is the better choice.

    But non-paper cutlery is a clear winner over paper cutlery. So then one would need to use the dishwasher to clean cutlery only, which seems pretty wasteful.

    "It's not easy being green."

  13. Brent_Eubanks | | #13

    Yes, but see my comment


    Yes, but see my comment above. Changes in the assumptions can easily skew the results the other direction. I doubt that the error bars on any of the values used in the study are small enough to reasonably say "only barely, under certain conditions". Again, this is not a criticism of the study, just the framing of some of the conclusions.

    Regarding cutlery, note that some modern dishwashers have a third, shallow rack for cutlery (rather than the traditional basket) and have the option to run just that sprayer so as to wash utensils without running a full load.

  14. user-1087436 | | #14

    Let us now praise famous nerds
    There it is. Once again we are given a long, well-researched article by MH, which he then has to defend and discuss until 10 at night, all day tomorrow, and probably into next week. And all this while working on his next project, commenting on other posts and continuing to field questions in the other forums: a guy writing in with multiple .pdfs showing his new 20,000 square foot "green" home, asking "Please tell me which framing system to use because the builders are coming on Monday"; someone asking how to choose an energy-efficient light bulb; someone else asking a question that Martin has answered a hundred times already. Indeed it is time to praise famous nerds, and the worthiest (and nerdiest?) of them all is undoubtedly Martin H.

  15. GBA Editor
    Martin Holladay | | #15

    Response to Jan Juran
    Thanks for the link to the list of energy-efficient dishwashers maintained by CEE. I have edited my article to include a link to the CEE list.

  16. GBA Editor
    Martin Holladay | | #16

    Response to Brent Eubanks
    You make a good point. If any of the assumptions in an energy life-cycle analysis are not quite right, the conclusions can certainly be different. Here is a list of reasons why china might not come out as well as assumed: many china coffee mugs never get used 30 times -- they just sit on the shelf. Many dishwashers are operated when half full, so it takes more energy to wash the china cups than assumed. Many china cups are broken before they are used 3,000 times (the presumed life span of a china cup, according to one analysis).

    And here is a list of reasons why paper cups may not be good as assumed: the cups may require more energy to manufacture, or may travel farther, than assumed (as you point out). Some paper cups may get damaged and discarded before they are used. Some people may use twice as many paper plates or paper cups as necessary, because they always double-up the plates to counteract their flimsiness.

    The point is not that any of these analyses are (in the phrase made famous by Mona Lisa Vito in "My Cousin Vinny") "dead-on balls accurate." The point is that there is no clear energy advantage to using china plates and cups, and that therefore disposable plates and cups probably don't deserve the scorn of environmentalists.

    I agree with your conclusion, of course: "The basic takehome is valid - you have to reuse the cup many, many times for it to break even." Thanks again for your comments.

  17. user-984364 | | #17

    CEE & topten
    CEE is great - and don't mistake it for "just another energy star list." Although for dishwashers there seems to only be 1 tier, for things like refrigerators, Tier II and Tier III go well beyond energy star - a nice way to sort. is another good resource to find the best of the best -

  18. watercop | | #18

    A couple thoughts
    We have a 5 year old middling efficiency Bosch.

    We do pre-rinse with a shot of cold (well, really "tepid" water since Florida groundwater is 70*F+) and a swipe with a scrubby sponge to get the scraps off.

    I try to catch the Bosch when it is 2/3 - 3/4 full and run a "quick wash", which provides acceptable cleanliness in 1/3 the time ( and, presumably, energy of a regular or auto wash...I have NO idea the differences between "regular" and "auto", but both seem to need almost 2 hours compared with the ~30 minutes of a quick wash)

    My wife is masterful at jigsaw puzzles, so she can fit about 200 more utensils and china into the Bosch than I am willing to work through. Of course, if the Bosch is that full, it needs the turbo-galactic-flamethrower-cosmic-pots-and-pans-wash cycle to get everything clean. That seems less efficient than quick washing a partially filled machine.

    I insisted upon a ceiling fan in the kitchen primarily to be able to quickly air dry the clean but wet dishes. Plastic has low mass and heat capacity, so even if heated during final cycle, it has poor ability to evaporate remaining water - we have a lot of plasticware; kids school lunch containers and leftover tins.

    Bosch seems to remember previous cycle times while predicting current cycle time. If I remember to run water into sink long enough to bring up hot water as Bosch starts, cycle time for a quick wash is about 5 minutes less. It is advantageous to do this since our main hot water comes from a heat pump; much more efficient than resistive heat, so it pays to preheat the pipes bringing hot water to the Bosch. (we are on well and septic, so the odd extra gallon down the drain costs virtually nil)

  19. user-659915 | | #19

    "Quick wash"
    Curt, you may be assuming too much in proposing that the energy use of your Bosch is less on the 'quick wash' cycle - have you measured it? The high efficiency dishwashers generally achieve their performance by allowing the contents to soak for considerable periods during the wash cycle, thus requiring less energy to blast the debris off with the jets during the active part of the cycle. The quick wash will certainly not use a third of the energy of the full wash and may in fact use more. Depending on how the machine is programmed, omitting the lengthy soak cycle may require even more extensive use of the jets.

  20. MCooper | | #20

    Life span?
    We had an efficient, modern Bosch dishwasher here for about five years that stopped working (still ran, didn't clean the dishes well) and, according the repairman who came out, these dishwashers are only going to last 5-6 years. Something to do with all the lightweight parts that make them so efficient.

    In googling this question, the most consistent answer is 9 years lifespan for dishwashers. So, given that and given the embedded energy in the manufacture and shipping of such an appliance, how would that factor into the equation? It must offset the advantage of machine washing, but does it eliminate it?

  21. watercop | | #21

    Interesting point, James
    I haven't measured it per se, but I do have a 4 channel TED system, one of whose channels is the whole house, and my sense (in other words, no hard data) is that the Bosch's heating element is on much of the time during any cycle as evidenced by whole house kW during wash cycles. Our domestic HW averages around 110*F, so the dishwasher's boost element gets a workout.

    One very solid data point I can relate is that the dishes come out of the Bosch one heckuva lot hotter after any of the standard long cycles than after quickwash. The Bosch has no direct air heating element, rather it heats the heck out of wash water so as to warm the dishes for better air drying. Quickwash cycle is so short that dishes emerge only tepid. In fact, quickwash is the only cycle whose temperature won't warp PET plastic bottles and jars.

    If I really got into this, I could move a TED channel onto the Bosch and collect data for various cycles.

  22. GBA Editor
    Martin Holladay | | #22

    Response to Matt Cooper
    Many web pages estimate the average life span of an automatic dishwasher. Two web pages actually cite sources.

    One web page cites data published by Appliance Magazine in 2010, giving the answer as 10 years.

    A CBS news story cites a study conducted by the National Association of Home Builders (NAHB) and Bank of America ("Study of Life Expectancy of Home Components") that gives the answer as 9 years.

    If accurate, this information is discouraging.

  23. user-659915 | | #23

    Dishwasher life
    We remodel a lot of kitchens and I see a lot of dishwashers and other appliances that are anything from twenty to forty years old and still functioning. People want to upgrade before they fail mechanically for a variety of reasons: dated look, too noisy, rusted (though still functional) interior, and more admirably, to reduce energy and water use. This is like the great hybrid car debate - do we make do with the old clunker until it dies, in the grand old Yankee tradition, or buy the newest high-mpg model?

  24. betterways | | #24

    Don't have 12 place setting to wash!!!
    I'm also not a family of 4 which what I'd previously thought these studies were based on. So this is really not relevant to me.

    Another problem with such studies is that most people wash the dishes before they put them in the dishwasher with the water running full blast the whole time. Do they ever count all that water in these studies?

    Half of my meals are eaten from a bowl with a spoon. And I reuse my glasses for ages. I also wash and rinse in fairly small dishpans and pour the rinse water on potted plants.

  25. Mikey | | #25

    How to dry?
    So you've got a dishwasher full of 140° dishes after the final rinse. What's the best way to dry them? You've got to get rid of the heat and the moisture. If you just open the dishwasher and hit the sack, all that hot moisture has to be dealt with by the AC system. If you leave it closed, with the heated dry off, the AC only has to deal with the heat, slowly released into the kitchen -- the moisture drains as it condenses. What really is needed is an outside vent to exhaust the hot moist air during the drying cycle. But then there's makeup air... this business of living in an artificial climate gets very complicated.

  26. user-982477 | | #26

    Did the LCAs include the Dishwasher?
    Hi Martin,

    Terrific work, as usual!

    Matt actually beat me to my question, asking whether the embedded energy and other LCA factors within the dishwasher itself were included in the LCAs for ceramic table ware? If I need a new $1,000 dishwasher every 10 years -- golly, that's a lot of economic activity to bake into the equation.

    Since you've been through all the studies, can you clarify? Thank you!

  27. user-865595 | | #27

    Life Span of China
    Now I feel a whole lot better about the old china in our crockery cupboard. We never could agree on a new everyday set, so it a combination of 30 + years old (wedding present) and my husband's Auntie Dot's set (circa 1950). So that is probably an average of more than 10,000 uses for each item. The breakfast bowls in particular have done well.
    But glassware - Oh My! way too much breakage. However, your favorite beverage (whatever it may be) doesn't taste the same out of plastic.
    Actually we have a set of picnic cups ( the red tacky ones from the grocery store) that get put in the dishwasher after the picnic. It gets really funny when friends write their names on them at a big summer party, and then find the same cup at the next event.
    Now I know what to say - thanks Martin for doing the research.
    However I am horrified to hear how short our dishwasher's life may be . . . .

  28. stepco | | #28

    Who needs hot water?
    I have been hand-washing all my dishes in tepid (room temperature) water for years, with no ill effects. The water coming into my house goes through a tempering tank, to bring it up to ambient temperature and avoid the unpleasantness of icy-cold water (42 degree incoming, in upstate NY) on the hands. This temperature boost cools the house very slightly, which puts tiny additional load on my wood-fired masonry heater in the winter, and in summer is accomplished for free.
    I think the 140-degrees of a dishwasher is not hot enough to kill bacteria anyhow, for those of you with sanitary concerns....

  29. GBA Editor
    Martin Holladay | | #29

    Response to Linda Foss (Comment #24)
    It sounds like you are washing your dishes in a way that conserves water and energy. So you are all set.

    On average, a dishwasher will use less energy and water than washing by hand. But it's certainly possible for a homeowner who uses a dishwasher to use more energy and water than a frugal hand-washer -- especially if that homeowner uses a lot of running hot water to rinse the dirty dishes before placing them in a dishwasher.

    As a wrote earlier -- you can wash dishes badly (or wastefully) using either method.

  30. GBA Editor
    Martin Holladay | | #30

    Response to Michael Armstrong (Comment #25)
    According to your analysis, when you use the electric-resistance element in the dishwasher to dry the dishes, all of the moisture that is removed from the dishes ends up condensing inside the machine and going down the drain. But I'm not sure you're right, for a couple of reasons. I'm not sure that the dishwasher compartment is completely airtight during the drying cycle; it's certainly possible that some or all of the moisture is vented into the kitchen. Secondly, I'm not sure that dishwasher manufacturers provide a cold surface during the drying cycle to encourage condensation -- something that would be necessary for your theory to hold.

    However, I'm unsure of the percentage of moisture removed by the "hot dry" cycle that goes down the drain, and the percentage that is vented into the kitchen. I'd be interested in hearing from any GBA reader with more information on the topic.

  31. GBA Editor
    Martin Holladay | | #31

    Response to Pam Kueber (Comment #26)
    Q. "Were the embedded energy and other LCA factors within the dishwasher itself included in the LCAs for ceramic table ware?"

    A. I don't think so, although some of the energy life cycle analyses I referred to were only available in summary form, so I'm not entirely sure of the answer. The point you bring up is important. Families living without a dishwasher avoid all of the embodied energy in the machine itself, which is clearly a good thing.

    Although these types of analyses are interesting, they all fall short of being definitive, because every such analysis includes many assumptions that are questionable. Many analyses assume that most Americans are going to want to have a dishwasher in the kitchen, at least for special occasions, and so the analysts may have felt justified in ignoring the embodied energy in the appliance.

    When you come right down to it, few GBA readers are going to alter their dishwashing behavior very much, if at all, based on a life cycle analysis. Most Americans want dishwashers for just one reason: convenience. Even if it could be demonstrated that washing by hand saves energy, few Americans would switch to hand washing. Similarly, even if an analysis proved that paper cups and plates save energy, few Americans are going to abandon china.

  32. GBA Editor
    Martin Holladay | | #32

    Response to Richard and Miranda Menzies (Comment #27)
    Richard and Miranda,
    You wrote, "But glassware - Oh My! way too much breakage. However, your favorite beverage (whatever it may be) doesn't taste the same out of plastic."

    You might want to buy a few stainless steel cups and glasses. They don't impart any off flavors to your beverages, and they don't break when you drop them. (A caveat: I haven't researched whether stainless-steel utensils have a high embodied energy component compared to china.)

  33. GBA Editor
    Martin Holladay | | #33

    Response to Steve Paisley (Comment #28)
    It's possible to use room temperature water to wash dishes, of course, but there are a few downsides. Room temperature water is less effective at removing greasy residues from plates and cooking utensils. If you aren't using hot water, you end up needing to use more detergent and more elbow grease -- and sometimes more frequent changes of wash water -- to achieve the same effect.

  34. lutro | | #34

    So many factors
    Steve raises another of the myriad factors in this question. I don't think that you can hand wash dishes and get any significant heat sterilization, without massive hot water use and higher than average water heater settings. For most people washing by hand, the water isn't warm enough, and the exposure time of each plate, utensil, and glass to the hottest water is too short for sterilization.

    I think dishwashers can sterilize most dishes, having the advantage of relatively long times at higher temperatures. Steve disagrees. I'm interested in other opinions on this point.

  35. lutro | | #35

    Better studies needed
    Given the interest in these questions, and the number of articles on it that have appeared in many publications over many years, it's surprising that there isn't (Martin couldn't find) a study that measured the variations in human use patterns for dishwashers. The Stamminger study measured hand washing behavior for 113 people in 7 countries, and showed tremendous variation. Then it compared to a dishwasher averaging substantially better than the 2010 US Federal guidelines, and apparently run fully loaded. Martin has already said several times that there are many ways to be inefficient, and I agree. But comparing perfect dishwasher operation to real world hand washing is not illuminating, nor a good experimental design. Several of the other quoted studies used commercial dishwashers, which I take to be different than residential. Are they more efficient, or less so?

    While it is certainly true that the majority of the population won't change their behavior easily, I bet that a big portion of the GBA readership would modify what they do, or how they do it, if they had good data on a better way. For us, the average of the general population is less interesting than the energy and water use in the better examples of both hand washing and dishwasher use. But as several readers pointed out, we need to compare the options that we actually have- not every meal a Thanksgiving dinner for 12, but rather the dish washing needs for our family of two, your family of three, that bachelor, or her family of four people, eating perhaps two meals a day at home, on average, with minimal cooking for one of them. Getting even a rough analysis of the variations in dish washing energy use for the diverse real world methods of people on this forum would be fascinating.

  36. GBA Editor
    Martin Holladay | | #36

    Response to Derek Roff (Comment #34)
    Dishwashers are not capable of sterilizing dishes. That's OK, though -- sterilization is not necessary for food safety. If you are working in a medical laboratory or a hospital operating room, you have to worry about sterilization. But not in a kitchen.

    The food service industry differentiates between "sanitizing" and "sterilizing." Here's an article that explains the difference: "It May Be Cleaned, But is it Sanitized?"

    Commercial kitchens and restaurants use dishwashers with high-temperature (180°F) rinse water. As far as I know, residential dishwashers do not use 180°F rinse water -- nor do they have to.

    This raises a medical question: is the obsession by some Americans who think that we need to sterilize our environment improving our health or harming it? Evidence is increasing that when babies and toddlers are allowed to have contact with germs, dirt, and farm animals, they grow up healthier and with fewer allergies than children who are raised in an over-clean environment. But that discussion must wait for another day.

  37. GBA Editor
    Martin Holladay | | #37

    Response to Derek Roff (Comment #35)
    You're absolutely right that it would be great if researchers could get funding to study how Americans actually use their dishwashers: how much water they use to rinse soiled dishes before putting the dishes into the dishwasher; whether the water used for pre-rinsing is cold water or hot water; and how often dishwashers are operated when they are only 1/3 or 1/2 full.

    I'm always in favor of more energy research. It would be good to have more data.

    Almost undoubtedly, Americans use their dishwashers in a way that requires more water and more energy than assumed by researcher Rainer Stamminger in Germany.

  38. JonathanBeers | | #38

    Foam cups
    Thanks, Martin for the article. Michael Brower and Warren Leon wrote about the demonization of foam cups in their book: "The Consumer's Guide to Effective Environmental Choices: Practical Advice from the Union of Concerned Scientists".

    Here's an excerpt from my (unpublished) review of the book:

    "Sweat the big stuff, not the trivial. How you travel to the grocery
    store is much more important than paper vs. plastic vs. reusable bags.

    Devote your energy to avoiding the most harmful activities, and you
    can stop feeling guilty about the occasional styrofoam cup or
    plastic fork."

  39. user-2511396 | | #39

    Shermans vs. Tigers
    Ah, the age old question of good enough vs. perfect. It's Sherman tanks vs. Tiger tanks all over again. Kind of like Pretty Good House vs. Net Zero House. Conisering the past, no surprise the Germans picked perfect and then disparage results that get the job done good enough but not perfectly. Don't tell me how much water the highest user used. Tell me how little water the most efficient hand washer used. Teach people how to wash that way. People have been known to learn things, although how to make money from that is the tricky part.

  40. lutro | | #40

    more on bacteria
    In my previous posting, I oversimplified/overstated the case for sterilization in a dishwasher, and even overstated my own view of it. After welcome correction from Martin, I've done more research. Obviously, with deep sea creatures able to thrive in volcanic vents at more than 1500 degrees F, and many atmospheres of pressure, killing all possible life forms in a dishwasher is impossible. Hospitals use autoclaves to sterilize some instruments, at temperatures above boiling and atmospheric pressure.

    On the other hand, 140 degrees F is the temperature of pasteurization, which has been used for more than a century to kill sufficient bacteria that it substantially improves food storage and public health (although some people argue about that latter). As a specific example, Legionella is killed by half an hour at 140 degrees. The bacteria responsible for cholera (Vibrio spp.), and related intestinal infections, are apparently killed, for the most part, at temperatures below 140 F, in times under 10 minutes. I couldn't track down any quantifying of the anti-bacterial effects of dishwasher detergents, beyond the assertion that they increase the types and quantities of bacteria killed at residential dishwasher temperatures.

    So while dishwashers certainly don't do anything like thorough sterilization, the do kill some types of bacteria important to food-borne health problems, and substantially decrease the quantities of other important ones. This contrasts with what is possible via hand washing, and that is the thrust of my point. Hand washing of dishes uses lower temperature water, has much shorter exposure times to the highest temperature water used, and uses milder detergents. For those who care about admittedly partial measures, residential dishwashers have an advantage in bacteria reduction.

    It's interesting to me that when I lived in Europe in the 80s, many European washing machines had a maximum temperature option of 90 or 95 degrees C, for the apparently large segment of the population who wanted to largely sterilize their clothes. Yet the plates on which we put our food, and the utensils which we put in our mouths, weren't addressed by a similar residential product option. Apparently, neither the public nor industry considered dishwashing to be as risky as clothes washing.

  41. AMJPhillips | | #41

    Countertop Dishwashers??
    I've been doing some research on countertop dishwashers to see just how they compare to full-sized units. The energy saving comparison between the two seem huge.

    I have a portable unit that I've had for more than 5 years. It's not been cleaning the dishes very well lately and even though I have cleaned the dishwasher itself, I am wondering just how long it's going to last.

    I found some energy saving info on countertop units that sounds too good to be true.

    I can't imagine paying less than $25 a year! Does anyone else have one of these and is this right?

  42. GBA Editor
    Martin Holladay | | #42

    Response to Annette Phillips
    This type of device is worth considering for some people, but your review isn't too encouraging: "I have a portable unit that I've had for more than 5 years. It's not been cleaning the dishes very well lately."

    And, glancing at the photo, I'm guessing that a lot of people will say, "I'm not putting that in my kitchen."


  43. lutro | | #43

    Another reference on "sterilizing"
    I just found an additional reference on the sterilizing potential of home dishwashers. As addressed in other postings, true sterilization does not occur, but the level of bacterial kill can be very high. The article says, "Microwaving sponges killed 99.99999 percent of bacteria present on them, while dishwashing killed 99.9998 percent of bacteria."

  44. GBA Editor
    Martin Holladay | | #44

    Response to Derek Roff
    Thanks for the link. Again, I don't think there is any evidence that home kitchens need to worry about sterilizing dishes; in fact, an overemphasis on sterilization and antibacterial products may be injuring human health.

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