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Comment by vanderZwan | Hacker News Reader

> Despite all the caveats, dishwashers are not only the convenient answer to our modernist woes, they’re actually more energy- and water-efficient than hand washing. A full dishwasher can clean 144 items with roughly 13 litres of water, or anything between eight and 20. According to a study by the University of Bonn, hand washing the same load uses, on average, 100 litres of water.

I genuinely wonder how people get up to 100 litres of water, or if my intuition regarding nr. of items vs water volume is just that far off. Are we sure this isn't measured by comparing to people using a constantly running tap for this instead of filling up one sink for washing and one for rinsing? Because I was pretty shocked to discover that most of my friends use a constantly running tap while washing the dishes.

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The article GROSSLY misstates the findings of the University of Bonn study.

Yes, many people around the world wash dishes under an open tap in a manner that can use 100+ litres of water.

But if you're filling a sink tub with hot sudsy water, soaking and scrubbing plates, and then rinsing them in a second tub of cold clear water (and even a squirts from the spigot), you're using about the same amount of water as a dishwasher.

The dishes come out as clean or cleaner (the detergent's less effective, but you can scrub where the dishwasher cannot, and for tough stains you can use appropriate treatments), and there's far less wear on plates, glasses, and flatware as you're not using harsh chemicals and abrasives.

If you have a large household or really don't like hand-cleaning dishes, go ahead and use the dishwasher, especially a modern one, and follow the tips. If you don't mind doing dishes by hand, or only have a few items (and need to wash them for next use), handwashing in the sink is plenty efficient. There are far worse consumers of water and energy.

I went searching, because it does sound like quite the quotable claim. Almost everyone who talks about the efficiency of handwashing seems ultimately to be referencing the same paper[1], although virtually nobody cites it.

The peak of the distribution of water usage is in the 40-50 litre range, however a nontrivial number of people use an absolutely enormous amount of water. The paper gives some observations about different approaches to washing, although it doesn't describe them systematically.

[1] https://www.tempurl4.uni-bonn.de/forschung/haushaltstechnik/...

>my friends use a constantly running tap while washing the dishes.

I realize this will sound whiny and justifying water wasting, but I am including tech solutions...

1. My hands are busy and filthy while I am washing dishes. I don't want to touch the handle. = Give me a foot controlled valve.

2. My kitchen faucet literally takes 2 minutes to get hot water. = Give me instant hot water (to a precise temp that won't burn me).

3. More water pressure makes it faster to clean food off and speed is of the essence when you are doing this chore. = Pressurize the water.

On a side note, I have determined that being the one in a relationship that takes full responsibility for the ever ominous dishes chore allows me to do less overall chores without complaint from my partner.

1. Quick search: https://www.amazon.com/Best-Sellers-Home-Improvement-Touchle...

2. You can get a water circulator that moves hot water to the cold water pipe until it gets hot. I haven't met a plumber that has recommended them though.

You can get foot valves[1]! And I think they're wonderful, I wish every faucet had them, and infinitely better than fighting with sensor-operated ones. You can pretty easily use half or less water while doing many sink-things.

[1]: https://www.google.com/search?q=foot+operated+faucet

> I don't want to touch the handle. = Give me a foot controlled valve.

If you want to save a bit of water, you can get faucets that are "touch" controlled (on/off). That way you can touch the faucet with your wrist/forearm/back of hand to turn it on/off. Temp is controlled by the knob position so it stays the same temp through on/off cycles until you move the knob.

Try insulating your hot-water pipes if you've not done so already. Wrap with foam or apply a spray-foam sealant.

(This requires access to the plumbing, of course.)

Foot-pedal taps are available, though they're more commonly a hospital item.

>I genuinely wonder how people get up to 100 litres of water, or if my intuition regarding nr. of items vs water volume is just that far off. Are we sure this isn't measured by comparing to people using a constantly running tap for this instead of filling up one sink for washing and one for rinsing?

A quick search says faucets run between 1.5 to 2 gallons per minute. That works out to 13.2 to 17.6 minutes of water. Dividing that by 144 items works out to 5.5 to 7.3 seconds of "on" water per item. That's on the high side, but not unreasonable if you're doing a through rinse.

More often than not [at least where I happen to live in the US] I actually see kitchen sinks with only one basin (and often too small). One basin isn't really enough to efficiently clean dishes without it being a big hassle.

I suspect that this is a multifaceted consequence of dishwashers becoming so commonplace, people cooking less and less, and constant attempts by owners to cut minor costs at the expense of tenants' standard of living.

If you want to save more water/have only one sink: only put a little bit of water in the sink and rinse with the tap (not constantly running of course) into the washing sink.

Not really much more trouble and you're always rinsing with clean water.

> instead of filling up one sink for washing and one for rinsing?

Most people I know have one sink. Two sinks were found in rich peoples homes.

Personally I really want one of those big commercial sink faucets that's a flexible shower head suspended by a spring BUT turned on by a momentary foot pedal instead of a squeeze valve on the head. The you have both hands free to rinse and scrub while your foot operates the faucet.

> Most people I know have one sink. Two sinks were found in rich peoples homes

My tiny student apartment had one, but other than that even the social housing I've lived in had two. My experience is limited to slightly older housing in the Netherlands and Sweden tough, so the other commenters point about smaller sinks being a consequence of cutting costs might still be valid.

Also, provided there is enough space this can be done in a single sink too: wash all items first, then rinse them. Speaking from (student) experience.

we actually have two sinks, but one sink is misused as as a drying rack because there is no other space.

not having hands free to turn water on and off is also an issue i ran into resulting in letting water running more often than necessary.

saving water is not all that matters. actually, saving soap is a lot more important. the more concentrated the dirt and soap is in the water, the harder it is for the biological wastewater treatment to work.

i can't find the reference but i remember reading an article in a german magazine lamenting about exactly that problem, suggesting that people don't use enough water instead of to much.

as a consequence, i prefer to spend more time scrubbing and rinsing and trying to remove as much dirt as possible without using soap, and only add a bit of soap at the end to remove the remaining oils that scrubbing can't get rid of.

given how much soap some people use when handwashing, the dishwasher may still be more effective on average, but i wouldn't use one just to save water.

>saving water is not all that matters. actually, saving soap is a lot more important. the more concentrated the dirt and soap is in the water, the harder it is for the biological wastewater treatment to work. i can't find the reference but i remember reading an article in a german magazine lamenting about exactly that problem, suggesting that people don't use enough water instead of to much.

That link would be worth its length in gold for me to show my spouse!

I don’t even have 144 items in my kitchen, I don’t think, so that’s probably a lot of dishwashing. It could happen if you lane the water running the entire time. I’m horrified to think that some people do that.

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