[bluGill]

Geothermal water heating just barely works out in general because efficiency drops with higher temperature differentials. If you would accept you water at noticeably below body temperature it would be great (though I suspect this is ideal for bacteria growth) efficiency. If you want your water as warm as the minimum recommended temperature by efficiency experts you are already in questionable efficiency range. If you go hotter it gets worse.

[makomk]

Yeah, reducing the temperature on water heaters is a great way of causing Legionnaire's disease.