Studies say that a horse watered with the auto waterers will drink up to 20% less than he would out of a bucket or trough. This has to do with how horses prefer to drink, one big slug followed by little sips. I'll look it up in my NRC if anyone is interested in the particulars. Basically, horses won't wait for the waterers to fill back up to completely satisfy their thirst, and some horses don't like how shallow the pans are compared to buckets. Some food for thought .