For 46+ years and counting I have used various and sundry methods of hot water heating. I have had lots of cold showers, too. Unless I was in Jarabacoa or Constanza, it was no problem, but i was a LOT younger then.
I have had shower-head water heaters for close to 40 years with very satisfactory results-with the caveats expressed by Chris above, and others-and important energy savings.
I have had an on-demand propane water heater, which, while very efficient, was also very costly, even when propane was cheaper. No more.
I have had and still have, medium sized electric heaters. they can be useful if you have a good source of electricity 24/7....However, there is an important pair of caveats: They can be very expensive if people leave them on all day and night (1) and I have heard that they can explode if the water goes off and they turn into boilers, rather than heaters!! (2)
Oh yes, I have put hoses on the roof, too!
I think, with the new technology and materials that are available, a combination of shower-head heaters, Tinacos on the roof, and a good solar heater, you would be more than well supplied.
HB