Is it More Efficient to Hand Wash or Use the Dishwasher?
Cooking from scratch is an integral part of preparing meals from your home food pantry. Unfortunately, cooking from scratch also means extra dirty dishes, pots and pans! Recently I read an article on the U.S. Government’s ENERGY STAR web site that claimed, “If you wash dishes by hand you are wasting more then just time…” (https://www.energystar.gov/index.cfm?c=dishwash.pr_handwash_dishwash; January 31, 2016)
I thought I would double-check this claim, which is based on the ideas that using the dishwasher saves money and time, provides better cleaning results, saves energy and water, and so helps to save the environment. This caught my attention because while today’s dishwashers use less water than older models, they also run longer to make up for using less water. For example, our new dishwasher uses 2.5 – 6.4 gallons of water to run a load instead of the 7.0 gallons our old dishwasher used. However, our new dishwasher runs nearly an hour longer at 130 – 135 minutes per load instead of 76 minutes! What’s more, run time estimates assume that the hot water arrives in the dishwasher already heated to 120 degrees F. If the water arrives at a cooler temperature, our new dishwasher runs even longer to heat the water before washing.
The Cost of Running the Dishwasher
The yellow energy tag that came with our dishwasher states that we can expect to spend $25 a year on electricity and/or natural gas if we run four normal loads of dishes per week. This works out to around $0.12 per load for electricity and/or natural gas, assuming that our hot water supply consistently delivers water at the required 120 degrees F. For our calculations, we assume that normal loads use around 5 gallons of water since we only run full loads. A quick look at our utility rates shows that the cost for 5 gallons of water and sewer is currently $0.03 in our region. This means that we can reasonably estimate a cost of around $0.15 per load to run the new dishwasher.
If conserving water is the most important thing, washing dishes by hand can conserve heated water as effectively as a dishwasher if about the same amount of heated water is used for either approach. When this condition is met, washing dishes by hand will always save energy over running the dishwasher for two reasons; (1) washing dishes by hand eliminates the use of electricity to run the dishwasher and (2) hardly anyone will hand wash dishes in water as hot as 120 degrees F! Most people like dish washing temperatures to be similar to the temperature of a hot bath, around 100 degrees F. This second reason is often overlooked.
The Cost of Hand Washing Dishes
If the groundwater is at 60 degrees F, this means we heat the water by 40 degrees F to hand wash dishes instead of heating it 60 degrees F to wash dishes in the dishwasher. Using the calculations at the “Ask Mr Electricity” web site, we estimate that it takes us around $0.06 to heat 5 gallons of water 40 degrees. This, plus the costs of water and sewer adds up to around $0.09 per load to hand wash dishes. (http://michaelbluejay.com/electricity/waterheaters-figures.html; January 31, 2016)
Following the process outlined below, we have found that we can meet the lower water consumption goal. We use dishpans to limit water use and rarely rinse dishes under a running faucet. Sometimes we use heated tap water, but an even better option is to use water from our rain barrels that is heated in our solar ovens.
Dishpans for hand washing dishes
Comparing Hand Washing vs the Dishwasher
Are the dishes washed in the dishwasher cleaner than those washed by hand, as the web site claims? Well, we don’t leave bits of food behind when washing dishes by hand. That is the reason why so many people rinse dishes before placing them in the dishwasher. We use vinegar in the rinse water to help get dishes squeaky clean. We use bleach if needed to sanitize the dishes, whereas it takes extra energy to run a dishwasher’s sanitize cycle.
Are there any hidden costs that the web site does not account for? Last I checked, cheap white vinegar, bleach and dish washing liquid cost much less than dishwasher detergent and rinse aides. The government website also fails to mention that a dishwasher is an expensive appliance to purchase! It could take decades to recoup the cost of a new dishwasher, and I doubt if a new model will last that long. Dishpans are cheap!
Will using the dishwasher save time? Not if we have to wait 2 hours to run the last load of the day before turning in! We can hand wash a large load of dishes in close to the time it takes to rinse and load them into a dishwasher, and have a nice chat with family or friends while doing it.
And so, contrary to the ENERGY STAR web site, we have concluded that washing dishes by hand is still much preferred to running the dishwasher, as long as a little attention is paid to the process. My simple cost comparison below assumes that one load of dishes is washed each day. However, when you are processing and preserving food, you may need to do several loads in a day – further adding to the savings. And even better savings can be had if you are able to use harvested rain water and heat that water in a solar oven!
Estimated Yearly Cost for Washing Dishes (7 Loads Per Week)
1. Dishwasher, Normal Cycle, Heated Rinse, No Dry Cycle
(Not including the cost of detergent, rinse aide, or the dishwasher for that matter!)
$55.00
2. Washing Dishes by Hand using Tap Water
(Not including the cost of dishwashing liquid and vinegar, dishpans or water heaters.)
$33.00
3. Washing Dishes by Hand using Rain Barrel Water and Solar Ovens
(Not including the cost of dishwashing liquid and vinegar, dishpans or solar ovens.)
$0.00
Instructions to Hand Wash Dishes using Tap Water
Materials
• 2 dishpans (15 quart capacity rectangular plastic pans)
• Dishcloth
• 2 tablespoons dish washing liquid
• ½ cup cheap white vinegar (bought by the gallon)
• 5 gallons comfortably hot water
Instructions
1. Fill one dishpan with 2 gallons of comfortably hot water and add the dish soap.
2. Fill the second dishpan with 3 gallons of comfortably hot water and add the vinegar.
3. Wash the dishes in the first dishpan; rinse in the second.
4. Use the dishwasher racks as a dish drainer and let dishes air dry.
5. When finished, hang the dishcloth to dry on the faucet or some other convenient place. Then rinse the dishpans and set them aside out of the sink to dry.
Instructions to Hand Wash Dishes using Rain Barrel Water and Solar Ovens
Materials
• 2 dishpans (15 quart capacity rectangular plastic pans)
• Dishcloth
• 2 tablespoons dish washing liquid
• ½ cup cheap white vinegar (bought by the gallon)
• 2 large pots to heat water
• 2 solar ovens
Instructions
1. Heat a large pan of rain water in each solar oven until the water is uncomfortably hot but not boiling. This can take some time. Be very careful when carrying the pots of heated water into the kitchen.
2. Fill one dishpan with the first pot of hot water. Add the dish soap and cool tap water as needed to make the water temperature comfortable.
3. Fill the second dishpan with the remaining hot water. Add the vinegar and cool tap water as needed to make the water temperature comfortable.
4. Wash the dishes in the first dishpan; rinse in the second. Wash the least dirty dishes first.
5. Use the dishwasher racks as a dish drainer and let dishes air dry.
6. When finished, hang the dishcloth to dry on the faucet or some other convenient place. Then rinse the dishpans and set them aside out of the sink to dry.
Below is pictured a load of hand washed dishes from breakfast and canning 10 pints of broth.
A full load of hand-washed dishes
Thanks to Lois Harper for participating in the [Grow] Network Writing Contest.
We’re still getting the list of prizes lined up for the Spring 2016 Writing Contest. We awarded over $2,097 in prizes for the Fall Writing Contest, including all of the following:
– A 21.5 quart pressure canner from All American, a $382 value
– A Survival Still emergency water purification still, a $288 value
– 1 free 1 year membership in the [Grow] Network Core Community, a $239 value
– A Worm Factory 360 vermicomposting system from Nature’s Footprint, a $128 value
– 2 large heirloom seed collections from Baker Creek Heirloom Seeds, valued at $103 each
– A Metro-Grower Elite sub-irrigation growing container from Nature’s Footprint, a $69 value
– 2 copies of the complete Home Grown Food Summit, valued at $67 each
– 3 free 3 month memberships in the [Grow] Network Core Community, valued at $59 each
– 4 copies of the Grow Your Own Groceries DVD video set, valued at $43 each
– A Bug Out Seed Kit from the Sustainable Seed Company, a $46 value
– 4 copies of the Alternatives To Dentists DVD video, valued at $33 each
– 4 copies of the Greenhouse of the Future DVD and eBook, valued at $31 each
COMMENTS(43)
You are leaving out the best part of washing by hand. The pleasure of just having warm water running over your hands and the fun of washing. I get so much pleasure in washing dishes by hand it is like a meditation. Each home I’ve had I get rid of the dishwasher and put in a cabinet. Just to note I am over 60 and still love it.
I totally agree. I have a window to look out of and a bird feeder on the deck to watch the silly antics of several different types of bird that frequent my area. A totally uplifting experience.
Agree..washing dishes while looking out at Nature is the best..but I still want a dishwasher…
I am phasing plastics out of my kitchen, and have to hand wash the ones I have. Putting them in the machine degrades them, so that the nasty hormone disrupting chemicals leach into our food. Plus cast iron and wood should be hand washed. The rest..into the machine, so I am in the kitchen cleaning up a bit less than hand-washing everything.
Another benefit is that small amounts of some beneficial residual species are not completely removed during hand washing.
And small amounts of pathogenic bacteria left behind stimulate the immune system causing it to become more robust. Another benefit overlooked, especially in this day and age of antibiotic resistance.
I have used both all 3 methods in my life time and prefer to wash by hand, either method. I currently have a single sink and do dishes when ever it is needed. I cook almost everything from scratch and I make a lot of things most people don,t like, ketchup and yogurt. I also can all summer and some in winter.
I live in a small village in the central BC mountains where limestone used to be mined so there is a lot of lime in and on everything. When I first moved I had a portable dishwasher. But I fast gave up using it because the water was so hot it baked the limestone onto the dishes.
Great article. Washing dishes by hand is also a way for people to work together. One washes, several dry.
And oh so much quicker than loading and unloading a dishwasher.
Often wondered about which is best. Thanks to Lois Harper for the time spent and the very informative investigative report. I wash dishes by hand, like my Mom did.
I have never believed that washing dishes in a machine is cheaper than by hand as it does not make sense no matter how you look at it. As the author states, the appliance itself costs a lot of money and can take years to recoup the cost.
I raised 8 kids which meant there were 10 of us if no one else stayed for dinner, which was not always the case. Ever cook for 10-20 people? The dishes will not fit in a dishwasher (along with the pans). And now that there is just myself and my husband most of the time (when kids and grandkids don’t stop by), who would allow dishes to pile up that long in a dishwasher? I wash dishes 2-3 times per day as I do not like dirty dishes piled in or around sink. It literally only takes 3-4″ of water to wash a few dishes and pans for breakfast or lunch, and same for dinner. There is no way a dish washer uses less water than what I am using.
Also, I do not see the sense of rinsing dishes and then washing them! That beats the purpose.
I am also not a germaphobe and know that being exposed to germs regularly is what keeps one’s immune system working properly. Obviously, if one is immuno-compromised, then a dishwasher with a sanitizing cycle might be good. but one can just as easily add a teaspoon or so of bleach to dishwater to get the same results.
Many people cannot live without their dishwashers, but I haven’t wanted one since I was a lazy kid of about 12. I enjoy the time to reflect. pray, think, and just have something to do. Doing dishes never takes more than 5-20 minutes, regardless of how many people one is feeding. Learning to do dishes as one goes keeps the sink from piling up before dinner.
That’s really thninkig out of the box. Thanks!
Thank you for this well-researched, thoughtful article, Lois! I don’t think most people have given a lot of thought to this subject lately…I surely hadn’t! One more consideration is that hand washing is more gentle to dishes and flatware — most old china sets (like the one I inherited from my grandmother) need to be handwashed for this very reason. I also remember reading somewhere that children living in homes where dishes are washed by hand have a better chance of developing fewer allergies. (This article cites the study done in Sweden: http://www.medscape.com/viewarticle/840268). Also love how you use your dishwasher as a draining rack. We have done the same at times!
This article is further proof that, while figures don’t lie, liars do figure. Several of the items which entered into the “comparison” between hand-washing dishes and using the dishwasher were actually variables which will vary not just per person, but also per location and time of year. For example, amount of detergent required depends on type of soil being removed as well as quantity of dishes; and groundwater temperature depends on location as well as time of year. The groundwater where I am (Colorado mountains) is barely above freezing this time of year (February).
Other items were not quantified in terms of cost, but were glossed over as if they’re free (e.g. solar ovens). The issue of time was also not kept to any standard of reasonable comparison, as a person can be doing other things while the dishwasher does its part, while that same person (or people) is fully occupied with both hands and eyes while hand-washing dishes. No value was assigned to the time of the person (or people) who are washing the dishes, as if their time is worthless, an assumption with which I cannot agree. The issue of wear and tear upon the skin of the hands who must handwash dishes was also glossed over/not addressed, as was the cost of skin cream, moisturizer or gloves needed to prevent deterioration of the skin on the hands of the manual dishwasher.
All in all, the article demonstrated nothing but a collection of unsubstantiated and unverifiable numbers which were used to make a point which was clearly preordained prior to the writing of the article. A true comparison would hold variables to a minimum and make an attempt to have a “control” situation, as well as document the specifics which entered into the calculations (energy rate per kW, EnergyStar rating of dishwasher, etc.).
Propaganda which counters government propaganda might get people thinking for themselves – or not – but it’s still propaganda.
In response to Sandy, kindness doesn’t cost a thing. To disagree with someone in a kind spirit goes a lot farther than calling them a liar.
I agree 100% . I was always taught in life that if you don’t have anything nice to say, then, don’t say anything. There are better ways to “speak your mind” & disagree with others with respect and to not antagonize others. Ponder on the meaning of the words “respect” and “tact” and try to use it next time, Sandy. Just saying. Yes, kindness does not cost a dime.
love this site … so much helpful information
how do you cast a vote for articles … i gave up trying a year ago … my vote never sees to get counted … very frustrating – not to mention – not fair!!!
Hi jaywalk – Sorry you’re having trouble. At the very bottom of the article, right below where the author info is, you should see 5 stars followed by “Rate this.” Sometimes it doesn’t work on slow internet connections…
As to REAL cost, it’s not even a question — hand washing (and drying and stacking) can BUILD a family while the magic electric slave called the dishwasher (which never really works unless the dishes have all be pre-cleanned before being given over to the new magic electric slave, a slave who enslaves us by mass Wall St brainwashing) just makes noises.
Back in the day, after a meal, a family would rise up and get together and create a small production line. If no one complains, the job of cleaning up after a big meal can be done in a few minutes. Plus the family has the opportunity to talk to each other, while using their hands and doing something productive. One person scraped, one washed and rinsed at the sink, one dried with a towel, and one stacked the pots and dishes in their resting place in the pantry. Everything was done in a few minutes (and I mean everything cleaned, dried AND returned to their places in the pantry). And the family got to talk quietly while doing a common chore, parents could catch up on kid’s gossip about this or that or whatever. While washing dishes, it’s a different kind of conversation than occurs than the more sparce and formal kind of talk at a dinner table. (Talking is harder with a fork in your mouth …) So there was lots of positive social interaction after dinner. IF your kitchen and living space is designed with proper allocation of space, i.e. with pantry and shelf space to store pots and plates, then there is no question hand washing is faster and more sanitary. If there are just two of you, and cooking is kept simple and it’s even faster.
Now compare that family interaction to the effect of the dishwasher. First of all, everyone puts on their earphones (to drown out the noise the dishwasher makes) as they go their separate way. Secon, the imaginary electric slave inside the dishwasher doesn’t really wash the pots and dishes, unless they were installed already prewashed by the REAL dishwasher, which is the real human who washed them before handing them over to the imaginary electric-slave inside the new dishwasher. And, once they’ve been prewashed by the real dishwasher, i.e. the human, as required for the imaginary electric slave inside the dishwasher to finish the job, it’s only a few seconds more time to rinse, dry and stack the dishes, if the family is still functioning as a family.
Once the dishwasher gets loaded, and it gets turned on, that’s when the noise starts. In a small house, the noise is so annoying IMHO, that a family cannot have a quiet conversation together. It’s like trying to have a conversation while someone is running a vaccuum cleaner. Which is yet another gimick which creates a more unhealthy situation than the lovely sweet sound of a broom. Without the dishwasher noise, a family can even just share the joy of a few moments of silence together. Otherwise, the diswasher makes it gush, whishh, spinn, slamm, and bang noises … while the magic electric slave inside the dishwasher wastes water and power while … and actually does nothing, except deprive the family of the chance to share a simple and effortless common chore and keep a kitchen and pantry orderly, and a house clean! The real human dishwasher, who had to load the machine had already done 90% of the work, having “pre-cleanned” the dishes before loading them.
And then let’s not forget the effort that it takes to unlaod the dishwasher and put things away. After an hour or two. By then everyone is onto another project. But, if it’s not unloaded and cleaned and disinfected, the dishwasher becomes the ongoing place where pots and plates are stored. Unfortunately, because the dishwasher is (a) closed (b) warm (c) moist (d) doesn’t get sunlight or free circulation of air and (e) etc, the dishwasher is probably the most unclean space in the house. It’s a fact that the typical toilet bowl is cleaner than the dishwasher. Because it gets sunlight and air, where plates in the dishwasher don’t. If it’s not unloaded, then the plates and silverware and pots we use for the next meal, are stored in what is potentially most unhealthy and unclean place in the house.
Sorry for the long post … one of my favorite subjects …
It’s also worth noting that many items cannot (or at least should not) be washed in a dishwasher. Crystal must never be washed in a dishwasher, nor fine china, nor anything with gold or sliver plating or trim. Even inexpensive wine glasses can become unattractively “etched” by dishwasher washing. Revere Ware, possibly the most popular brand of stainless steel cookware strongly advises against washing in dishwashers, something I was unaware of until about 10 years ago (I’m 69). I find that rice starch simply will not wash off a pot in our excellent quality dishwasher, although it comes off easily with a sponge in a sink of hot, sudsy water. And forget about casserole dishes, especially if cheese was involved.
Great research!
I definitely prefer hand-washing. Even if I lived off-grid, I wouldn’t want to waste electricity. The production of electricity and of appliances has an environmental impact – something the government website does not consider. In warm weather, unheated water works just fine for washing dishes. Also, when it comes to cleanliness, I think our hands do a better job than a dishwasher!
If I didn’t have a dishwasher, I would not invest in such an unnecessary expense and waste of space. As I got tired of pulling dirty dishes out of the washer, I now hand wash/scrub and then wastefully run the washer primarily to rinse off the soap.
I re-use most of my dishwater to water the trees in my backyard, so there is another savings as well as being prudent with water use during our time of drought. I can use completely non-toxic soap doing dishes by hand, as well as essential oils, but it is harder to find non-toxic dishwasher soap. It is not (legally) possible to re-use the water from a dishwater. What is not taken into consideration into the equation is that the production and manufacture of a dishwasher is enormously wasteful, requiring mining, industry production, and malls and stores to sell them in. Washing by hand wins every time in my book.
In 37 years of marriage and raising 9 children, we had a mechanical dishwasher for exactly 7 months. Don’t feel the need for it.
You can read the same type of argument for paper vs. cloth diapers. I’m sure glad I had cloth diapers I could wash when we had no money to buy paper ones!
Here is a poem which changed my attitude toward doing dishes as a young wife:
“Thank God for dirty dishes
They have a tale to tell
While others may go hungry
We’re eating very well.
With home, and health, and happiness
I wouldn’t want to fuss.
By the stack of evidence
God’s been very good to us!”
I keep this posted over the sink and listen to mind-stimulating radio programs while doing dishes. The children learned cooperation and leadership at the same sink, and none have wanted for jobs.
if you use biodegradable dish soap you can then water plants with the dishwater, further conserving resources.
This was a fantastic comparison, one that you obviously put some time and effort in to! Our dishwasher broke (the day before Thanksgiving when MY ENTIRE FAMILY came for the holiday) and I have been washing dishes by hand ever since then. I have been wondering if its really worth going and purchasing a new one and your article has really opened my eyes. Thank you! Another option is to water your plants with the left over water, provided the dish soap is organic and the vinegar won’t kill them. Excellent article!
Dishwashers are hard on dishes. My crockery and cutlery is staying in better condition now that I’m hand washing, especially the glassware. The dishwasher has left permanent marks on my stainless pots
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Fantastic article. I have been hand washing my dishes and drying them in my defunct dishwasher for 18 years. My kids keep bugging me to replace the dishwasher but it isn’t going to happen!
Not only that, but my dishwasher won’t clean pots and pans and so I still need to pour handwashing water to do that and to wipe down the counters and appliances. And my dishwasher is only a year old.
I love the calculations that Lois went through to figure out costs. She is a also very thoughtful when researching the information. Well written, too. To her cost conclusions, convenience conclusions, and environmental considerations, I want to add another facet to consider.
I read recently that hand-washing is a better way to clean dishes because it can help boost immune systems due to the few remaining bacteria that are on clean dishes. In some ways that might be true, but if a household has an immune-compromised person, then a dishwasher might be better. As most readers of this site probably know, our over sanitizing of everything in our houses, and on our bodies, has resulted in lowered abilities to fight off infections because many viruses and bacteria mutate to defend themselves from the very agents we thought would protect us. So I agree that a few germs left on dishes would be fine.
That said, there should be some consideration of the soaps/detergents and other agents used in dishwasher tabs and gels. These commercial products have also evolved…and not in a good way. Big brand names have way to many chemicals to be healthy for anyone. The same can be said for the hand washing products that strip the oils from hands and leave them chapped, cracked and “rashy”. So any discussion of costs and results should involve the comparison of natural products vs. commercial, chemical ones. (I noticed that Lois’ hand washing dish soap is a very good natural one! Kudos there.)
Over all, I appreciate the analysis of this seemingly simple question.
Thank you for sharing all the money-and-time-saving-ideas articles. I enjoy reading everything. It always encourages me to think of alternative ways of doing things at home & how to grow my own food to save money & time with more beneficial results. So thank you, once again.
I never thought I would see an article with instructions for how to hand wash dishes. I grew up in a family of seven and was washing dishes by hand from the time I was so small I needed to stand on a chair to reach the sink. I never had a dishwasher and never wanted one. I can live with a few residual germs rather than toxins from a detergent. I like to keep things simple.
Dishwashers may also increase the incidence of allergies and asthma. The dishes actually get “too clean” so we fail to exercise our immune systems in a healthy way.
Thank you for an interesting article. To sanitize dishes, I prefer to add a few drops of tea tree oil which is a much healthier option. Bleach is bad for the environment and more importantly plays havoc with our immune systems.
I don’t actually sanitize dishes as I agree with those that posted that the germs stimulate our immune system. I saw the tea tree oil used when I was on a meditation retreat as they were using it to comply with health and safety regulations in the UK 🙂
Wow. Thank you for crunching the numbers. I have never quite believed that the dishwasher was the labour saving device people claim. Esp. since I have had two that were not reliable about creating dishes that I felt were clean. It takes extra time, which I sometimes resent, but I much prefer to know my dishes are clean vs sporting sterilized left behind food bits.
Oh I so agree. I’m not very “politically correct” and I tell people that I have a Mexican Dishwasher. It’s called “MANUAL” Hahaha! I also use my dish water for all kind of things from flushing the toilet to watering plants. One helpful thing I would like to share. I do use an electric clothes washer. Almost never use the dryer as I hang clothes to dry. (I do sometimes used the dryer on no heat to tumble some things and it also helps to remove lint) Here is what I have done for nearly two years. I have a number of 5 gallon buckets. when I wash clothes. I put the drain hose in the bucket and save all the drain and rinse water to use for flushing the toilet. It really saves a lot of water by using water that would go down the drain twice before it exiting the house. Also, if you have a septic as I do. It prevents the sudden influx of water into the septic which can harm the biological operation of the tank. I took classes on septic systems so that I could service my own. Where I live you are required to have your septic checked every 6 months. It costs $250.00 to have professionals do it. I took the classes which cost $175.00 and got my license to perform my testing myself. My license is good for 2 years. After that all I need to do is take the classes again and upgrade my license. To me, using wash water to flush the toilet is sooo much better than using good drinkable water from my 350 ft. deep well that has some of the best tasting water I have ever had! Cudos to you on the dishwashing article. One other positive point I would add however is if you are like me, and work every day getting really dirty hands that normal washing doesn’t get clean…. Do a load of dishes by hand and see how sparkling clean they will get!
One other benefit of handwashing is using the dishwater for other cleaning when you are done. I use it to clean something different every load. One time it might be the refrigerator shelves. One time, the cabinet fronts. I even use it to scrub the floor. This of course depends on the condition of the water left over when done washing dishes. 🙂
But dishwashers are so convenient, leaving time for more important matters!
Paleo Martin
The articles were very interesting – not all washed up!
Good article but one point of contention: warm or hot water is needed to actually clean the dishes but there is no point in using warm or hot water for rinsing those now-clean dishes, cold water removes the soap more quickly. However, if the dishes coming out of the dishpan still have a greasy residue due to dirty dishwater, then you should use hot water (not warm) since the cold water will leave a bit of that film behind.
I save the oily things for last when washing so I keep my soapy wash tub water clean longer for this reason. But if the dishes coming out of the soapy dishpan truly are clean, there’s no need to waste warm or hot water. Same is true for rinsing clothes, by the way, that’s partly why they provide the cold rinse cycle.
A couple of caveats –
1) if you tend to use too much soap (so many people do!) then really hot water will remove more of the “trapped” soap which is why food service establishments rinse super hot, due to the liability of soap residue.
2) Porous surfaces can trap soap, so very hot water is best there as well.
But, in both cases you’re using very hot water, hotter than you washed in.
You can test the cold water business when you dump that soapy dishpan in the sink at the end – try getting the soap out of the sink with hot water, it takes quite a while. Next time, try it with cold and it’s tidy in a snap. Fact is, it would take some extreme measures to remove all of the soap all of the time anyway, we’re all used to consuming tiny quantities of it. How much is too much, I don’t know, but it isn’t gastrointestinally pleasant from what I understand!
I know the conventional wisdom is to use hot water when hand washing dishes, after my time as a lab technician in the Navy, I quit doing so. There is no way to get the water hot enough to effect any organisms. So heating the water is a waste to me. In the winter I will heat the water a bit, but only enough to take the chill off it.