I was talking with someone for whom I have created a BOB last week. The family went camping in West Virginia, on land rented by a neighbor. There was a building on the property, and the neighbor showed them how to turn the water, etc. He also said that if anything happened in the city, they were to just go there. So, it set up my next question, which was "and how long will it take you to leave?" Anyway, I told her I was making them BOBs for the family.
One of the things she told me is that she, a woman with hair down past her shoulders learned to shower with about 1.5 liters of water when on a trip in Africa.
DW might have a problem with that because she tends to take 20 minute showers. However, she also was happy that she had the kind of wipes in her BOB that she thinks would allow her to clean up without a shower. I finally got DW to look in her BOB and add some clothing to it.
Since I got off track, my point was if you are talking about taking a shower in a situation when you don't have much water, then the answer might be not that you don't need much water at all. Otherwise, you might be going without any shower.
Finally, what about one of the solar shower bags. If you wet down turn it off, soap up, then rinse off, you should have a decent shower for one taken with no plumbing. Might not work for Hacksaw or me in winter, but it could work in other circumstances. See:
http://store.sundancesolar.com/sosh5ga.htmlCampmor has something for a few bucks less. I wonder if something could be made like this that could withstand being in hot liquid itself. If you put the bag in hot liquid, got the content warm, then showered, it might be a good systems. You'd need a big pot, but my brew pot could handle it easily.