There are in-line water heaters that work or gas or
electric.... very popular in Europe as you don't have to have a tank.... solar
heaters http://www.diynetwork.com/diy/pl_water_heaters/0,2036,DIY_14194,00.html and
the The Jan issue of the Horse Journal addresses portable hot water... I'm
not going to copy the whole thing, but here are a few choices:
