I agree with Smrobs on this one...tying a frightened horse, can actually enhance his fear, because when a horse is afraid, he wants to move his feet. So having him on a lead rope, in an enclosed area like a round pen, or small paddock, so you can just move with him, while keeping the water running, and allowing him to move around you, and figure out the water's not going away, nor does it hurt, is usually the most effective route. There are other trainers who will simply snub them up good to a solid post, and just set back a good distance, and just spray the ground around, and eventually the horse, until he figures it out for himself that it's not going away, and eventually stands there.