Good info!!! Sometimes we forget what can be done with what we may already have. This is "on demand". Great to do in winter, if we need the hot water.
I suggest that if it is sunny, a container in the sun can produce warm, if not HOT, water for use. In fact, right now we all have to run the water out of our hoses carefully to not be burned -- if they are in the sun -- water tubs become bath water.
I remember reading somewhere (on this forum or some other?) about someone building an outdoor shower using a couple of 5 gallon tubs on the roof of the shower for heating water in the sun. It got so hot they had to put another bucket filled with cold water so they could mix the 2 and avoid scalding burns.