I camp a lot in summer, and no way no how am I getting out of the showers in the communal toilet block to go to the lav and then traipse back again only to find me shower's been nicked.
I strongly suspect I would be unable to - I am completely unable to wee in the sea, I could as a child, but not as an adult, so I suspect the same would apply.
Why would I (we) need to, we have an en-suite wetroom for us, an en-suite shower room for guests + an en-suite wet room downstairs again for guests + a separate cloak room, so don't see the need!
True, but the amount I need to use is small in comparison to the amount I'm saving by reusing the shower water. I'm a Yorkshire lass, through and through. :o)