When boondocking for a long period (more than a week) we wash the day's dishes in the evening in one tub and rinse them in another tub with heated water and then quickly use the warm rinse water to partially wash bodies or maybe just head/hair. As others have said the dish water is used to flush toilet before bed time. When taking a shower, my wife uses a bit more water than I do for a shower, but I can pretty easily take a shower with 1/2 gal of water. I may not be ready to go to a fancy ball, but then I haven't seen any to go to when we are boondocking.
All this conservation of water can become necessary because our trailer only has a about 12 gals of fresh water.