An excellent hand held camping shower can be made by adding a vent tube to a 2 liter water bottle:
BTW: I use Pert Plus (shampoo+conditioner) to wash my hair and whole body. This is because it rinses off quickly.
Step 2: Adjustable Cap
Cap can adjust flow rate for a longer shower.
Water can be warmed in the sun or on a camp stove.
I live fulltime in a motorhome and have been using this shower every day for over two years and it saves me lots of water and energy.