Yeah my argument is that this is nonsense. Just turn the tap off often when you’re scrubbing the dishes (use the water for rinsing) and it should be obvious that you’re using less water — particularly when you take into account the fact that a dishwasher uses 4 gallons of water no matter how many dishes are in it.
Under ideal conditions perhaps a modern dishwasher comes out ahead, but again maybe the ideal Rambo bird-killing-machine cat is also capable of decimating local bird populations.
How did I measure it? I had the DW drain into a bucket.
The DW won hands down. I also learnt to wash dishes without the water running when I was a kid.
Yes, the proviso that you should only run it when it is full is important, but I assumed everyone knew that.
Cities often have systems, we're in rural Australia and are water conscious- as far as dish and clothes washing go that's grey water discharge which goes onto a near house mulch pit for household rottables and garden waste, the water that reaches the pit bottom hits a crushed stone bed with slotted pipe that drains water to above the vegetable garden and fruit trees (between the leach drains ) where it moves through the soil making tomatoes, potatoes, figs, oranges, lemons, grapefruit, etc.
No dishwasher, no tap running - but regardless of how much water we use in the kitchen none of that truly goes to waste, if we use more we just put less on the garden from the same source tanks (which are all level gauged).
Mulch on garden with microplastics is likely ok as plants extract the minerals | elements they need.
I'd have to sample and check.
A great deal of our clothing, bedding, towels, etc is natural fibre in any case.
Where it probably falls down is where they have dishwashers in office kitchens where they don't fill it up and chuck it on anyway so they have their favourite coffee mug ready for the morning.
So I would argue dishwashers are demonstrably more efficient than hand washing dishes. Whether that means better for the environment is an entirely different question that has to take into account manufacture and use.