I've had great succes with the frozen water tank problem by putting one of
those heating plates they use for raising chicks underneath a plastic 100 liter
waterbin in the stables
these are low voltage ( 12 V) and there is no contact with the water, you
can keep the transformer safely away from the horses, these plates hardly
consume any energy but give off enough heat to stop water from freezing - we've
had -15°C here last winter and this worked fine. With lower temps you might want
to use a slightly wider & lower bin so the top layer won't freeze
Ofcourse our pipes freeze up anyway so I still haul water but at least the
troughs won't freeze..also found using big 3 gallon galvanised garden watering
cans and making more trips is far less tiring than using the big plastic
containers which are impossible to carry.
(and in spring the plate moves to the chickencoop to keep the chicks
warm)
I've also tried using infrared lamps hanging over the bins but the
horses tried to play with them unless they are really really high up
