Hand wash vs dish washer
 

According to "The Home Energy Diet" by Paul Scheckel, which I'm currently reading, there was a study done at a German university on this. They had volunteers wash 12 place settings and also had a dishwasher do the same. The results were:

.	Volunteer	Dishwasher
Water usage	27 gallons	4 gallons
Water Heating	2.5 kWh	1.5 kWh

I found this pretty interesting. I didn't think hand washing was THAT much less efficient. It also states that "about the dishes were were judged to be 'really dirty' or at least not acceptable to be placed on a dinner table, while the machine dishwashers offered consistently cleaner dishes".

I'll remember that next time I have 12 place settings sitting there, but to use 27 ga;;ons of water you would have to have the tap running nearly the whole time! I take the largest pan or bowl that needs to be washed, fill it with hot soapy water and wash, until I have a pile of clean soapy dishes, then I rinse those and keep washing, 27 gallons would be nearly 13 minutes of letting the faucet run at full blast (1992 Federal Energy Policy Act, 2.2gpm or less from all faucets), so I'm not sure who they had wash their dishes, but this study seems a bit skewed.

That is quite ridiculous. Somebody needs to tell the designers of that study what a sink plug is and what it's used for.

What are you guys talking about? Are you telling me you're not suppose to flood your kitchen while you do dishes? How am I suppose to keep my floors clean if I don't? Huh?

pfff...and you guys call yourselves DIYers.

I like to think of it as the opposite of the difference between a bath and a shower :)

Someone needs to teach those people how to wash dishes! I can only imagine that the tap was running completely open and they didn't plug the drain while washing or rinsing.

Those numbers are so skewed as to seem almost rigged. Can anyone find a link to that study?

Tim

I'm guessing they just picked up random people to do them. Of course any energy concious person could use much less.

I have never seen someone wash dishes with the faucet on the whole time, but my room mate has said that her parents do wash the dishes that way and that they are not about to change their ways, I just know that i grew up in a house where we didn't waste water as we had to pump it by hand out of the ground, carry it in to the house, heat it on the stove and pour it in to the sink, you get to lazy to be wasteful, of course now that water comes out of that magical pipe in the basement in to a water heater and flows in to the kitchen you don't think about it until you get the bill then you are just baffled as to how it costs that much!
Anyway, the average sink is around 14x16x7 a large sink is that is 7.2 gallons of water, with what this study said is used you could fill the sink until it was full to the rim 3.75 times... I now understand why we have issues with water.

I saw a report on TV about some ecological people. The first one was leaving in city and was renting a room to a foreign student. When she was interviewed she immediately said that what is the more shocking is that she can get only one 5 minutes shower per day. She has the habit to stay at least a quarter of hour under the shower without stopping the water at any moment. Now she has to stop, and start, and stop, and start... the water. I had the feeling that each time she was saying "stop" or "start" it was costing her so much.

Other advices seams so silly to me, per examples to stop the water when you are brushing your teeth, to stop the light when you are leaving a room or when there is enough natural light...

People are people and they won't take care about what they don't know the cost.

Denis.

I just measured my kitchen sink (each side ~ 13.75" * 14.75" * 5") and did a rough calculation of volume (rounding down for rounded corners and sloping bottom) ~ 4 gallons. I can usually wash all the dishes from one to two meals in less water than will fill one bowl of the sink. So I can wash 4 settings of plates and/or bowls, cutlery, glasses, serving and cooking utensils, pots, pans, etc. in approximately 4 gallons of water.

I may just make a more rigorous study of this. It's geeky, but hey all in the name of efficiency!

Tim

That would be pretty cool to see Tim. :)

If your 4 gallons figure is accurate, then the dishwasher described by the OP is a better way to go... assuming that you can pile all the dishes from the day into and run it when full.

And assuming you don't rinse stuff first.

Interesting.

If I ever get around to buying/installing a dishwasher, this will be much more relevant! :)

As nasty as it sounds, if my (single, bachelor) Father didn't have a dishwasher, he'd be wasting more water than you can imagine, cleaning up what happens when dishes sit for a week or more.

Instead, he puts the dishes in the dish washer, which apparently inhibits mold growth, or at least hides it so no one notices... :)

Once he's getting low on dishes, he adds soap and turns the machine on, and it cleans/sanitizes his dishes. When they come out, they look just as good as new.

It has a built in water heater, so it's not piped to the hot water supply in the house.

The energy star web site says an energy star dish washer uses 5.8 gallons or less and 1994 or older as much as 8 gallons to be energy star... not all dish washers are energy star, but even at that that is almost half again more then the 4 gallons stated in the study and most people I know have dishwasher that are well over 15 years old.

Hi,

I have a Bosch dishwasher, and not only does it use very little water (around 3.5 gallons, I think?), it heats up the water in the machine (using cold water), it has no heating element (so you can wash plastic items without melting them) -- the hot water evaporates with the latent heat, and it is extremely quiet, too. Oh, and it is all stainless on the inside, and there is about 2" more height available inside than a typical unit, so you can fit more into it.

Bumping this thread since I've been giving some thought to this problem lately. I've read/heard quite often that dishwashers use less water than hand washing, and each time I reply "That depends on how you wash".
This article has a similar statement to that in Paul Scheckel's book:
Unfortunately, the link to the PDF appears to be broken.

But how do I hand wash efficiently? I mean, what can a dishwasher do that I can't? Googling doesn't bring up much more than I already know, like this page: Maximizing Hand Dishwashing Efficiency in 5 Easy Steps. The first step (Use two sinks) got me thinking that using a bin instead would ease the collection of grey water for toilet flushing. This would save water, but more globally, the dishwashing process itself would still use the same amount.

I read a while back that a certain dishwasher model stores an amount of grey water to use for pre-rinsing the next load, which supposedly reduces overall water usage.

On the other hand, I usually use hot water only for greasy stuff, while the rest only get cold water. And rinsing is cold, too, to save energy.

It's really really easy to see how much water you use, first step is to plug both drains so nothing goes down the drain, then wash your dishes.
I've washed an entire counter of dishes using a small mixing bowl full of water (about 4 cups, quarter of a gallon) and rinsed using the same amount of water, so half a gallon total, I'm not sure how a dish washer could use half a gallon of water for what ends up being about 4 place settings worth of dishes and the pans used to cook the food.

I think dishwashers are one of the most advanced and cheap energy efficiency devices around. Hard to beat.

Yep, I rebuilt an engine out of a Honda Civic, some time back. When I got it back from the machine shop,and before re-assembly, I put the block in the dishwasher, and ran the pots & pans cycle on it to make sure there were no stray bits from the shop.

I got over 130,000 miles before I finally sold it, too.

Indeed, dish washers are hard to beat.

-AC_Hacker

Did You dry it in Your "Solar Powered Food Dryer"?

I had a cheapy portable dishwasher--the kind that you hook up to the faucet. I stuck the plug in before starting it up once to see how it did. Doing a full load of dishes (way more than a 4-person place setting), it almost, but not quite, filled up the sink.

Seriously, though... people let the water run the whole time they shave just so they can rinse the shaver every once in a while. How do You think they wash the dishes?

I can't wash & rinse a 4 place setting in 4 cups of water. I suppose I could in 10l (~2.5Gal), but I sure can't do it at 156.2 degrees F. This $200 dishwasher can: Danby Countertop Dishwasher - Walmart.com ( reviews: Danby DDW497-W White Energy Star Electronic Countertop Dishwasher DDW4 )

Besides, washing dishes by hand rates a bit higher than folding underwear & socks on my to do list.

I suppose in survival mode or when it is necessary to use a biodegradable detergent (I don't know of one that works with dishwashers - LET ME KNOW IF YOU DO) and disposables are not an option.

BTW I don't know if AC_Hacker was joking about washing an engine in a dishwasher, but I know of a payphone company that washed malfunctioning coin mechanisms from payphones in a dishwasher. Worked great to prevent coin jams due to grime buildup.

I don't have a dish washer and I wouldn't go out and buy one because it would "save water" because it wouldn't, not for me and not for a lot of folks, but just like AC hacker, I wouldn't mind having a dish washer in the shop, right next to the oven that could be used for powder coating metal (cleaned in the dishwasher of course) and the microwave that is used for drying wood.

Aw you guys, We have lived the last 13yrs full time in our converted greyhound, and we have a fully automatic dishwasher, it is very versatile, it can even type stuff like this, and drive the bus.
When we get the house a little further along (ie roofed) a dishwasher will be one of the first power tools we get.

A quick search for biodegradable soap for dishwashers I found.
Dish Soap -Dish Detergent -Dishwasher Detergent -Dishwashing Liquid | Seventh Generation
Biodegradable Dish Soap | Non Toxic Dish Soap | Eco Friendly Dish Soap | Cruelty Free Dish Soap

I have not tried any of them as I do not have a dish washers other than myself.

I do not think he was joking I know of a few people that have done this and it does work as long as the woman of the house does not find out.

A friend of mind told me that she lived with a roommate from Finland while in college and one thing she remembers is how natural saving water was for her. For example, she would do the dishes only once a day. During the whole day any dirty dishes would first get soaked, then easily washed in the evening.

I thought that using grey and/or rain water for soaking would allow the amount of water needed to be reduced. Then I remembered reading about a dishwasher which would use the grey water from the previous wash to soak the next load. Has anyone else read about this?

Thanks. They answered my question (not covered in the FAQ) about the usability/legality of use of their product on boats (not holding tank, but direct disposal of graywater). I;m not sure if I am allowed to paste their answer here, but the gist of it is they don't know about directly discharging into seawater cause there is lack of regulations for such use. Their products are evaluated for normal waste disposal "via waste water treatment plants" & "designed to biodegrade in the presence of bacteria" "and in water, bacteria is present in smaller quantities than on land" ..."do not contain chlorine or phosphates, both of which are detrimental to waterways and aquatic life. ...Our detergents are likely safer than their market counterparts, however I can not say with certainty to what degree, or if they adhere to the legal guidelines of directly discharging into water."

Good folks, though. Heidi said: "I appreciate your interest in our products, and your caring enough about the ocean to be wary of using harmful detergents." Actually , from what I gather, using "dow" & such (degreasers) is more harmful and can get You in more trouble than dumping oil/gasoline into seawater. Good product for what it is. Probably safe to use in holding tanks that rely on biological rather than chemical treatment, for dump stations that don't allow chemicals & for on site graywater disposal. They were quick to reply too. I just failed to post it until I got an e-mail that someone replied to this thread. (Piwoslaw)

Piwoslaw, haven't heard of such a dishwasher, but a good idea for RVs & such.

The first post says "heating energy" used. Does this include the entire cost of electricity to run the dishwasher? What about the cost of the dishwasher detergents you have to buy because you can't use Dawn (or off brand versions of it). I think we need a better study. My guess is dishwashers are more efficient if you are washing a large enough load and comparing washing the same amount of dishes in the sink at one time. What about washing the 3 or 4 dishes left after each meal in the sink.

My dishwasher has registered 1kwh three times and 2kwh a different time on my whole house power meter that only counts full kwh before it hops up a number. So over a kwh but under 2kwh. It's a bit of a dishwater amount but that includes all of the electricity from the pump, heater for the hi-temp wash option, and heater for the drying function. Basically the full normal wash with the options on. I'm not sure on the exact water usage because I always forgot and either washed my hands or did something else with the water while it was running but I know it is less than 6 gallons.

With those figures and how many dishes you can get into the dishwasher I can't see how hand washing could possibly use less energy. Pulling up hot water even once a day to do the dishes and rinsing them would be more water than doing a full load of dishes once you've gone through them all. Leaving the counter full of a dishwashers worth of dishes to wash them quick enough while the water is safely hot and rinsing the dishes with a minimal amount of water to make it more efficient would be a serious challenge.

Not to mention the newest Energy Star standard for dishwashers is now(as of January 20, 2012) <4.25 gallons per cycle and <1.372kwh per cycle(<295kwh for 215 cycles).
Federal standard <355kwh and <6.5 gallons.

The average 2.5 gallon aerated head on a sink would probably take 2 minutes worth of rinsing for a full dishwasher load of washing and that 5 gallon is already way over your water usage from the dishwasher. Not to mention the work and time going into doing the washing.

Asn long as we are turning our attention to the energy that can be saved from washing dishes by some alternate method... the incessant movement of water molecules should be recognized and utilized (seriously).

Just letting dishes stand overnight, submerged in water will do half the washing for you.

No effort...

No energy...

Just molecular movement.

-AC

I agree,
Twenty seven gallons of water is ridiculous.
the other thing that is not mentioned is how much energy was used to make the dish washer and the capital outlay that was used to buy the dishwasher.
Regards Whitworth

I LOLed at this study...Looks like they should visit some countries in the world where the daily water ration is 5 gallons a day or less...they find very ingenious ways to conserve water

I use the molecular version of dishwashing myself. I pour leftover relatively clean water on my dishes. And let soak. Often for days at a time to ensure that a minimum of soap and scrubbing is required.

Make Them Molecules Work, then Mod the Dishwasher!
 

Good going creeky, let the thermal energy in the water do most of the work.

But I realized that dishwashers might be improved, even modified to allow for pre-soaked dishes with less water and shorter wash times.


Here's a post from someone who built an Arduino controller for his afflicted Maytag. With most of the work already figures out, tweaking and optimizing should be really an easy matter.

Best,

-AC

just started playing with Arduino this spring. haven't really done much.

but this looks pretty nice.

I don't wash dishes...I use paper plates, then burn them in my woodburner! C'mon people, are you serious? Four pages of arguing which uses less water!!!!

Right now there are 7,021,836,029 people on the planet and they usually eat at least once a day.

If you lived in a jungle in the tropics and could walk up to a banana plant and cut a banana leaf for a plate and then when you were done, toss it back into the jungle to re-enter the bio-cycle, then dish washing economy really would be a fool's errand.

But there is a chain of industrial events that ends up with the paper plate that is under your food.

This argument is actually about something larger. Ultimately it is about taking responsibility for that chain of events.

Best,

-AC

Right - a LOT of water is used to make paper. One estimate I found says ~1/2 gallon per plate. Plus petroleum based coatings, and the fact that you cannot recycle a used paper plate mean that using paper plates means you are using more water than either hand washing or machine washing reusable plates.

My initial post was tongue in cheek-apparently I didn't make that clear. However, am I the only one here that thinks it's silly to see four pages of debate on which uses more water? About responsibility of the 'chain of events '- how much water(and other resources) was wasted by the power generated used to respond to my post, and take me to task? How many electrons, oil, water, and who knows whatnot, were spent to point out, on your phone or computer, that my paper plates are not "eco-friendly"? Doesn't it seem ridiculous, when carried to that extreme?
I have learned an awful lot from people like AC Hacker, Solar Mike, Doax, Neil Blanchard, and many others, and am grateful for the posting and sharing various ideas and projects. I like the exchange of ideas and thoughts, good and bad, and various discussions. But let's not become so focused on the goal that we lose relevancy. I think that is why an awful large portion of the general populace paints all conservationists with a pretty broad brush- and not in a positive way.
Now I'll stop my rant and go back to lurking.......

I'll admit that I had a feeling that you were joking, hence why I refrained from answering. On the other hand, you don't have enough posts here for us to get to know your sense of humor.

Anyhow, I'm sure there are people whose view of the world around them could be summed up by your previous post, so if AC's and Neil's answers help someone understand how things really work, then they were worth the extra electrons.