but you can't make him drink. I dunno I guess you could like get a firm grip of the horse's head and slowly ease him down towards the water if he's not rattled. You know, just push its lips and teeth into the water just in case it's being stubborn for the sake of it and desperately needs the hydration to make it through the day. Maybe, I'm not sure how strong horses are. This whole thing might just be straight up infeasible, you might like get a hold of it and find he's just too strong for you to move, I dunno. I guess it probably wouldn't really be a big deal if the horse trusts you but if it did that would be a little strange. Like, you own a lot of horses and don't really spend much time with this one and if it's really attached to or reliant on you, that might be just a little off, but not like it means anything its just a horse. yeah I don't know much about horses.
As someone who has worked with horses... strong enough to not let some mere human force their head into water if they really don't want to, or let you shove a funnel in their mouth for that matter.