my warm water hurricane shower (we haven't had city water disruption since the 70's and my hot water heater holds temp for about 2 days) is the use of a plastic garden sprayer painted black...keep track of the time in the Sun, as even with the thick poly sides it can get pretty warm... I use the regular spray tip, but have seen where some attach a larger spray head from a regular sink rinse hose... the sprayer tank is dedicated, no insecticides/herbicides

I ran a couple of experiments on solar heating that were reported on a couple of occasions... if anyone would like a repeat, please ask