Alright my first post in here.
I have been pondering whether or not to post this, mainly due to some costs involved in making it (and not sure of other folks budgets).
But I am sure if you cannot afford to then you can find a way to improvise (Rednecks and Southerners always do, I am a redneck).
Okay, no more twaddling....
Homemade water heater:
1. One tub or 55gal plastic/metal drum.
2. Platform of at least 7ft off the ground. (can be made out off anything wood, concrete, pipes, steel)
3. Greenhouse type plastic material. (poly-carbonate sheets or construction film "However, I'd stay away from it")
4. Second structure needs to cover the bathtub entirely with the poly-carbonate sheets placed on the structure.
5. modify the drain the your tub to allow for a smaller hose (garden hose or smaller) to be attached.
6. Thermostat with a 3ft long corded display. Place the thermostat in the tub and have a your reader down low so you can read the water temperature.
This idea is non-pumped or pressurized so if you want it to run into your house I would change the size and structure. But for an outside shower it works. Though you may want to build walls and a door unless its just you and the wife. And unless you can find a way to modify it (insulate or something) use in summer months, lol. Otherwise it may freeze.
You can use either a 55gal drum or a bathtub. The drum is cheaper and its plastic so lighter.
Or if you want a hot tub, try this.