I agree, and some of us do talk about water wastage. Also that of electricity, detergent and other cleaning products. Some Mumsnetters have talked about bleach, shampoo, shower gel, fabric conditioner and other product usage that seems alarmingly high to me (imagine the massive factories producing all this stuff and the enormity of the plastic bottles left over).
But you can't be too clean, according to MN. There's a thread running where some people are showering 3 or 4 times a day and several have confidently stated that 'everyone' showers twice a day.
There's people unashamedly using their tumble dryers during the current hot, dry spell even though they could easily line dry.
But it does need to be borne in mind that some things do have to be used many many times for the environmental impact to be less than single use, shopping bags in particular. People have those jute bags, they need to be reused thousands of times before the environmental impact is less than a single use plastic bag, properly disposed of, eg reused as a bin bag for non recyclable rubbish that is incinerated so never ends up being dumped in the sea.
You might find this podcast interesting about the nappies (spoiler, reuseables are better for the environment when all factors are taken into account, but not by as much as you'd think, although I don't think they mentioned using them for more than one DC, which I think would be a given, because even if you only use them for one yourself, you'd sell or give them away when you've finished with them).
https://www.bbc.co.uk/programmes/m001md4l