Because T is so electric current sensitive, I can't use my de-icer for the water tank. So what I do to get her to drink a lot in the winter is soak her feed, than I bring out a 5 gallon bucket of very warm water when she's 3/4 done her hay. Sucks it right down! I have resorted to adding salt to her feed without much results, though she does use the salt lick.
Walka get water in his feed, but he doesn't mind the temp of water in the tank so right now his water intake isn't a concern.
Regal Charm, like your suggestion about insulating the tank, going to give that a try, thanks.