I keep learning new stuff about dishwashers. Almost five years ago, I wrote about one misconception of how it worked that got removed when I saw a video taken inside one while it was operating. Now this article tells me that my practice of pre-rinsing before putting items in the dishwasher is not only wasteful of water, it actually leads to less clean dishes!
One of the arguments against pre-rinsing is that certain detergents are designed to cling to food particles, as the Cascade detergent brand informed The Wall Street Journal in 2015. Without a surface to stick to, your dishes won’t get as squeaky clean.
Consumer Reports offers another explanation. According to the product-testing magazine, newer dishwashers—those purchased within the last five years or so—won’t wash your dishes for very long if the sensors in the machine don’t detect much dirt in the water. “When that happens, the dishwasher gives them just a light wash, and items come out less than sparkling,” Consumer Reports’s Ed Perratore wrote in 2016. “To avoid that lackluster result, don’t rinse; just scrape off bits of loose food.”
…Sure, you can still scrape off big chunks of excess food or soak your egg yolk-stained plates in hot water first, but there’s no reason to rinse every single item before loading your dishwasher.
This advice seems so counter-intuitive but Consumer Reports is a pretty reliable source of information.
Surveys have found that Hispanic and Asian families tend to view using dishwashers as a sign of decadence, that people who use them look down on the honest toil of washing dishes by hand. In fact, it is not common for many of those households to use the dishwashers that are already installed as storage places for their hand-washed dishes.
The more thrifty among them also justify avoiding them with the argument that it is wasteful of water. That turns out to be another big misconception.
One mind-blogging statistic from Consumer Reports states that the average person wastes 6000 gallons of water a year by pre-rinsing. Most dishwasher machines use just 3 to 5 gallons of water per load, while the average person uses about 27 gallons when washing dishes by hand, according to The National Resource Defense Council.
That’s a huge savings of water.
D.C. Sessions brought an interesting point to my attention. With conventional coal which uses once-through water cooling, absolutely huge amounts of water are used by power plants for cooling, e.g. used as the cold sink in the Carnot heat engine. Some quick googling finds that a conventional automatic dishwasher uses approx 1000 watt-hours of energy per dish-load, and assuming a typical coal power plant with once-through water cooling, that corresponds to about 35 gallons of water “used” by the power plant. So, you might save overall water by hand-washing, although it’s pretty close, and it would depend on how you get electricity for that automatic dishwasher (power plants can be much more efficient with their water usage compared to once-through water cooling, at the expense of somewhat increased capital costs, and somewhat decreased thermal efficiencies and subsequent decreased electricity production), and I could be making mistakes in this rushed analysis.
I never understood the appeal of dishwashers. Another noisy machine that takes up space and breaks down. I’d hardly call washing dishes by hand “toil”, and once you have a system, it gets done pretty quick. And you can use the time to
ponder the mysteries of the universethink about what’s on the telly that night.I’m guessing I might use about that much water over a week. Based on dishwashers I’ve seen, the stuff I wash would comprise several loads. Whatever, I ain’t changing.
/Luddite
To Rob Grigjanis
For any automatic dishwashers which are any good, that might represent substantial time savings for housewives. I know that washing machines were an absolute huge boon to housewives around the world by saving huge amounts of their time. I was watching a TEDx talk on clothes washing machines, and I have a new appreciation for them now.
I can easily believe this. Our first child arrived about a year ago, and ever since we’ve been hand washing baby dishes and bottles and breast pumps and all sorts of little baby-related things on a daily basis, and it’s insane how immediate and extreme the jump in our water bills has been. 30% easily. At first I didn’t believe it could all be related to the hand washing, but it’s not hard to believe at all if you think about it -- all that time with the water running full blast for a fraction of the number of dishes that a dishwater can do. And our dishwasher isn’t every efficient at all (it’s almost 20 years old). If we had a newer more efficient model, I bet the percentage increase would be even more.
A nonsensical argument. If there’s no surface (heh, crockery ain’t surfaced?) to stick to, then it’s already clean.
And the putative alternative argument:
If the dishwasher washes until dirt is not detected, it follows that either way, the dishwasher stops washing when it can’t detect dirt. So, whence this putative difference?
I’d rather spend twenty seconds scraping grossness off the plates than have the dishwasher spend 10 more minutes using water and electricity. I call that a reason.
EnlightenmentLiberal:
The water vanishes after it’s used? I thought it just got hot, and possibly slightly polluted.
—
Rob Grigjanis:
Think of it as a washing machine, but for dishes instead of clothes. Exactly the same appeal.
(You wash your clothes by hand?)
(cf. #3 & @4)
“27 gallons when washing dishes by hand” is a sign of a broken system, one that doesn’t value precious resources. About 10% of that does me for the daily dish wash.
John @6:
Having done that on occasion in the distant past (bike tours), not bloody likely! That really is toil. I find washing dishes to be soothing, with the added bonus of knowing stuff is clean when I’m done.
Isn’t it always nice when people somehow assume that the person doing the dishes is
A) female
and
B) not working outside the home?
EL
Your argument doesn’t hold any water (haha) as power plants typically don’t use drinking water (defined as “ready to drink) a resource and don’t produce wastewater that needs treatment as a result. The water evaporates and goes back into the cycle.
To save water while washing dishes you probably need to setup a rinse sink. Maybe a slight variant on how restaurants do it.
You probably fill it just enough to dunk your first dishes in (start with the flat plates not bowls or glasses) and the first one you can move right to the drying rack. As the rinsing water held in the sink gets soapier you do a very quick rinse with the faucet water falling into the same sink so it adds to your dunking water and dilutes it.
Restaurants sometimes add another chemical to the rinse water to make the plates look good but this isn’t really necessary. They also start with a full sink of rinse water but I think starting small and using the faucet as necessary will be the most efficient.
Oh and for what it’s worth, my problem with dishwashers is things coming out still requiring a manual cleaning. Having unclean dishes in drawers and cupboards annoys me. Probably due to living with people who thought they only had to wash one side of each dish, pan or glass.
I guess I must be the only person who uses a handful of litres of water to soak all the dishes. I quickly and inattentively rub dishes in filthy water (really filthy, by the end), and then it goes in the dishwasher for the most Eco cycle.
No, I don’t have a water meter, I just hate the idea of wasting drinking water.
I’ve never successfully used a dishwasher to get dishes clean. I put them in with just stuff scraped off and they come out with stuff stuck to them still. Even from a dinner that ended 15 minutes before the dishwasher was run. And the food isn’t really sticky stuff or anything. I must be using it wrong, but nobody seems to be able to tell me what to do to get stuff clean.
So I hand wash things. It takes almost as long when you have to scrub the dishes before they go in the dishwasher anyway. Also, the dishwasher runs for literally 1.5-2 hours on a normal wash. That seems like excessive use of power and water. That’s without heated dry and whether I scrub the dishes or not, and the drying cycle is less than a third of the time it takes to run.
That said, I’d probably still install a dishwasher in a new house because it’s hard to sell a house without one in the US.
Oh and I don’t use the water full blast when washing dishes. Since the average faucet runs at 2 gallons per minute, and I have it on about halfway, in the 10-15 minutes I run the water to wash a batch of dishes, I use roughly 10-15 gallons of water. So less than half what they say the average person uses. And I tend to wash big things in that time that wouldn’t have fit in the dishwasher and required hand washing anyway.
How can anyone use 27 gallons cleaning their dishes by hand to begin with, let alone on average? My sink is pretty standard, and it holds about 20 liters of water. Those 20 liters can clean multiple days worth of dishes for me, though granted I do live on my own. But six times that amount of water to wash dishes by hand? I just can’t wrap my mind around it.
I do use a dishwasher, I can’t wash dishes by hand, due to a combination of skin and sensitivity problems -- the latter means I can’t feel to hold a soapy dish safely, either dropping it because I’m holding it too loosely or sending it shooting across the room if I’m holding too tightly.
Rob Grigjanis@#2
New dishwashers can be so quiet you wouldn’t notice they were on, I was staying in a cottage last week that had a reasonably new Bosch dishwasher that you couldn’t hear for most of it’s cycle, both of us checked it was on at different points it was so quiet. That dishwasher was also small maybe 40 cm wide? It still took two people’s crockery and pans for two days, very neat and well designed, I’ll be going for something similar when we need to replace our existing dishwasher.
How you load a dishwasher and using the right cycle make a lot of difference to getting things properly clean, but I rarely have any problems though our dishwasher isn’t new -- as I was given it I don’t know exactly how old it is, but I’ve had it for about seven years. We do pre-clean most things that go in it, or rather the dogs pre-clean for us, as the dishwasher will sterilise the plates even at it’s lowest temperature setting that works well for us and the dogs.
When I did wash by hand I started with 4 or 5 cm of hot soapy water and the glasses, rinsing with hot water into the bowl as I went so I know I rarely used more than a bowl full, definitely not 27 gallons!
Eh -- This compares the “average” person with a device that has gone through several rounds of optimisation. What they need to compare is the optimal hand wash with the dishwasher.
I grew up in a place/time where water was only available for 2 hours and had to be stored. My spouse grew up in a place/time where water was available 24 hours. There is a marked difference in how we wash/rinse dishes when doing it by hand.
To Giliell
I share your skepticism in this matter, but every source that I can find says that we’re misunderstanding something, and that power plant water usage is somehow a competitor to water usage for other uses, i.e. farming. Ex:
https://www.ucsusa.org/clean_energy/our-energy-choices/energy-and-water-use/freshwater-use-by-us-power-plants.html
I cannot explain it now. I also don’t understand. I need to look at it more.
Jazzlet @15:
Our Max could get the grottiest casserole looking spotless, given an hour or so. I do miss him, not primarily for his cleaning skills.