We have 120 gals fresh water. Here's what I do: stand under shower in head. Quickly get entire body and head wet. Shut off water. Shampoo/condition hair. Leave conditioner on hair. Soap up body. Put small amount shaving cream (or body lotion) on legs. Shave legs using pink throwaway razor. Once legs (and armpits) are done, run water again, and quickly rinse entire body. Done, and used very little water, but feel nice and clean (and smooth).
If a nice, hot day, you can do this same method on the stern platform with the stern shower. Daytime... bathing suit. Nighttime... whatever.
On our old boat, I have done this same method with a solar shower up on deck.
We also like Savon de Mer, all in one shampoo/soap that works well with salt water.
Here's to more women piping up on this thread!