A dishwasher is more efficient than hand washing under normal circumstances (not an ancient dishwasher, not pre-washing dishes, more than one plate to wash, etc).[1][2][3][4][5][6][7][8]
Edit: added citations and removed "IIRC"
[1] https://www.pcrichard.com/library/blogArticle/why-dishwasher...
[2] https://www.reviewed.com/dishwashers/features/please-stop-ha...
[3] https://www.treehugger.com/kitchen-design/built-in-dishwashe...
[4]https://www.realsimple.com/home-organizing/cleaning/more-tec...
[5] https://www.cnet.com/how-to/how-much-water-do-dishwashers-us...
[6] https://www.npr.org/sections/thesalt/2017/11/24/564055953/to...
[7] https://www.huffpost.com/entry/wash-dishes_n_7232216?guccoun...
[8] https://www.energystar.gov/products/appliances/dishwashers/d...
In addition, a dishwasher has high pressure pumps, a centrifugal grinder, and its own water heater (to heat hotter and more localized than a central water heater, above sanitizing levels)
* You don't need rinse water, so the total water needed is at least halved. Since the water is just sitting in a bucket, you can do many, many washings with the same water which increases that efficiency even more.
* You don't need heated water as sanitation and complete cleanliness is unimportant. Heating the water alone uses more energy than everything else put together.
* You don't need particularly clean water, just clean enough to prevent large dirt from adhering. As such you could use floor-cleaning chemicals that clump the dirt and precipitate it to the bottom increasing use time. Reusing water and the chemicals in that water for longer has a very large impact on the environment.
* a couple strokes with a bottle brush take way less energy than a high-pressure pump and once again, get the item clean enough.
* Fewer things going through your dishwasher increases its lifespan and decreases the total cost of operation. This is also better for the environment
please don't be so quick to judge when the individual's circumstances may be more complex than first assumed.
The only case where they might have any weight would be widespread collection of water to the extent that it had a measurable impact on the community, but this would involve large quantities of water and would almost certainly involve business interests rather than personal ones.
[1]: https://attorneys.lawinfo.com/water-rights/nevada/las-vegas/
Reducing consumption is the only answer, and further down is reusing. But recycling is so inefficient, I assume it has mostly been for political points, and conveniently, we had tons of containers going back empty to China.
I think they meant that they do it then they do dishes and have space for cleaning trash. In that case there is nothing wasteful in it.