For years I’ve been using a 3-gallon insecticide spray can as a portable pressure-water dispenser. You’ll find these in any hardware store. Simply replace its long gardening spray nozzle with an ordinary kitchen hand-spray nozzle and it’s ready to go. I use mine primarily as a cockpit shower, but it works just as well in a shower stall belowdecks. You can also use it for other purposes, such as rinsing off your dodger, solar panels, snorkel gear and dishes.
I painted my can flat black and usually keep it on deck where the sun can heat up the water inside during the day. On cloudy days or in cool weather, I heat up water on the stove and pour it in. One pot of boiling water added to two gallons of cool water produces a perfect bathing temperature. My shower can provides me with hot showers at anchor or underway, indoors or out, without having to run the engine to heat up water.