I've read that a dishwasher is less wasteful than hand-washing of dishes (perhaps this isn't true for people who are very, very scrupulous about their use of water while washing dishes, but that's not most of us).
By the way, around here (North Europe) we have special dishwashing brushes that apparently aren’t a big thing in most parts of the world.
[0] PDF https://web.archive.org/web/20091109165849/http://efficient-...
When you overload the dishwasher things don't get clean and then you wash by hand afterwards (in the case of pots/pans this might still be less water use just because when hand washing you are likely to drain the filthy water half way through)
I've seen people who scrub the food off by hand under running water before putting it in the dish washer - they are clearly using more water since hand washing plus rinsing the soap off is using less water than they use for the rood rinse.
That said, I would not expect a dishwasher can actually wash the inside of your straws so that is one of the things that should be reserved for hand washing. If you use a minimal amount of water in your wash sink, and a minimal amount of rinse water hand washing can be a low water use thing. Most people leave the water running for longer than they need to for rinsing and this wastes a lot of water.
Hot water usually costs a lot of valuable energy though.
and besides, not everything go in the dish washer. And moreover some the dish washer soap can attack the surface of many things => increasing the need to replace those things...
The water usage is almost a 10x difference and the power usage of handwashing is 2/3 more:
"A European study comparing hand washing to machine dish washing found that hand washers used as much as 27 gallons of water and 2.5 kilowatt-hours (kWh) of energy to wash 12 place settings, compared with the 4 gallons and 1.5 kWh used by a hyperefficient dishwasher to wash the same number of dishes."
https://www.rodalesorganiclife.com/wellbeing/washing-dishes-...
120L = 7 very full sinkfuls of my fairly standard size kitchen sink. 7! For 12 people's-worth of stuff!
I'm not myself concerned all that much about conserving water, but I am a normal person, so I don't wash my dishes under running water. I fill the sink up with water, stick in some washing-up liquid as it fills, then once it's mostly full (12-15L of water?) I use that. Total use per wash is then 12-15L. Maybe a bit more if I give something a rinse. (Very much optional in my view for most items - but some things do need it.)
You can wash a lot of stuff in that much water! So that's why I am a bit surprised at people using 120L to wash twelve places'-worth. That's eight times the amount I'd use for washing 3-4 people's-worth of stuff and all the items used to prepare the food in the first place.
Poor scalability!
(I think my dishwasher uses 17L per wash so I don't worry too much about using that instead. I am quite lazy.)