At the moment my horse is drinking between 15 and 30L a day. It depends on the weather really.
I have the anual a problem with pipes/ troughs freezing too so this year I put a trug bucket in the shelter in a rubber tyre with hay stuffed round the edges for insualtion. Because its a smaller bucket, my horse drinks less water but more often so the ice doesnt freeze thickly and Alli can break it with her nose. Its worked so far, but its only got as low as -8 or 9 degrees C.... I guess its colder in Canada!