A simple and inexpensive way to have a hot water shower in your boat is to remove one of the petcock drains from your engine and replace it with a hose nipple. You then get a good grade reinforced water hose with a sprayer on one end and slide and clamp the other end to the nipple.
I ran my hose under the floor board to the stern and back around through the side compartment. It is handy for the driver to hand it to the skier to warm up their hands at the end of the lake. You can also warm your bindings before skiing. If my feet get cold, I put them in a plastic dish pan with lake water mixed with hot water.
For those that wear a wet suit, it is great to heat up the wet suit before getting in the water or after you get out of the water.
The first boat I put a hot water shower in, I also installed a demand pump with a valved hose “Y” to be able to mix hot and cold water for a perfect warm shower. I’ll have to say this is a very nice way to do it, but does require more materials, more plumbing work and electrical work. All hot is not as nice, but a lot easier to install.