a couple of options for heating water during long term power outages... the black painted garden sprayer for pressurized supply... 125' of 7/8" garden hose holds about 2 1/2 gal.... a 2mil contractor bag laid flat, with the mouth sitting on and closed with a couple of 2x4s... 2 1/2 gal fills at a depth of about 1"... both the bag and hose got to better than 130F in one hour of July bright Sun light... the bag was dangerous to handle at that temp, and water needs to be removed with a dipper... the sprayer about 100F in the same time... ambient water temp about 75F