Our barn also uses soccer balls in the water buckets outside, so the horses can push it around to break the ice. They also break the ice every now and then and strain the ice out with a tennis racket.
Inside the barn, they have purchased insulated water bucket holders for a five gallon bucket holder. You can also use heated water buckets or the heating elements for the big outdoor troughs. Also, for a water supplier another barn uses a big water drum and made a box that goes over it, then they stuff it with hay/straw/rags and it keeps the water unfrozen.
Intermediate Rider~Learning Equitation and English Pleasure~Interested in Eventing
A horse will tell you everything you need to know about him, if you listen.