We have a 100l tank for showers toilet etc. and a 60l tank for drinking water, we also carry some spare water jerry's in our tow and even have a 12V pump for collecting shower water from creeks etc. We have considered adding another water tank, but after checking weights of van have decided to stick with what we have and make do with the 100l tank for showers. During a recent trip we discovered a simple water saving trick for showers.
When water is limited we have wet down, lathered up then washed off soap. This has worked well for a long time to save water, but we recently tried a commercial body wash product called "QV Gentle Wash" it costs about $19 for a litre, which lasts a long time and is OK to wash hair instead of shampoo. I have a chronic skin condition that means I need to shower every day and have to be careful with what I wash with this QV stuff seems ok on my "delicate" skin. Have not tried it on very hard bore water yet, but think ti will work better than soap, which in heavy Queensland boar water does not lather.
The process is wet down, lather with the QV Gentle Wash and then wash off, the QV cleans well and washes off really easily, more easily and quicker than soap. To our surprise we were using about ½ the water per quick shower than we did with our usual soap and shampoo. Hope this helps with some of you who have limited water supply as it has us. We both can shower each day and have doubled the days we can shower from the van's water 100l supply. Sorry if this sounds like an add, but my dermatologist put me on to this stuff and it works (note for medical reasons, I also have to use the "QV skin lotion" each day as after showering).
That's pretty much how we do it also when on tanks, wet down lather up rinse off. The other thing we do is if washing dishes while on tanks is wipe off any excess with paper towel, so your not wasting water rinsing.
I've been using that QV wash for years now, it's good stuff, keep a bottle in the van and the house.