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!
Our tank heaters cost $30 and keep a 100 gallon tank from freezing. If you have a plastic tub get the floating heaters, plug it in and then the water doesn't freeze. Our horses normally drink 10-15 gallons of water a day. 5 gallons equal 20 liters. So 40-60 liters per day in winter, more in summer.
Tank heaters are cheap horses need 24/7 acess to water my 3 horses go through 100 gallon trough in 2 days. Lack of water in winter can cause colic problems.When it gets cold and windy they drink even more.