We go out and break ice a couple times a day. There is no way to heat water tanks for cattle that are out on pasture 20 miles from electricity around here. There are solar heaters, but they're pricey. Just try to time your ice breaking right. Also try to make the horse empty the tank. Don't leave the horse without water, but also don't put 100 gallons in the tank, knowing the horse will only drink 10. I used to go out morning and night with an axe and pitchfork to break ice. Be sure to scoop the ice chunks out of the tank or they'll refreeze. Pitch the chunks away from the tank. Sometimes a piece of foam thrown into the tank will leave a hole for stock to drink.