You can’t force them to show gratitude. They’ll most likely give a nonchalant snort and start drinking at a leisurely pace, making you wait for them as if you didn’t have any other plans. If the horse is passive aggressive it will wait until you’re already at the water, not drink and then claim it was never thirsty. You both know you can’t force it to drink, and it would ridicule you for trying. Perhaps, you’ll resort to threats, reminding the horse that you’ve already replaced your dog and your butler with robots. There’s no reason you can’t reinvent yourself as the world’s first tequestrian by riding a robot horse. But it will remind you that the horse was a wild animal once and would gladly be so again. Then you’ll scream something about him once having sex with a donkey and it responds by kicking you in the chest.
You can induce birth in a heavily pregnant horse by showing it a snake. Just be certain there aren’t any cliffs about. Horses are more frightened of snakes than gravity. You can threaten your horse by saying you’ll send it to Guam if it doesn’t drink, even leaving brochures in your saddlebag as an added touch. He’ll hate you for it. As the saying goes, “You can lead a horse to Guam, but you can’t stop him from jumping off a cliff.”