Sometimes a horse doesn't like the water because it gives them a shock in a place where they hurt. I have noticed that with my horses.
I will probably annoy quite a few people with this one but:
My IR horse sweats like somebody did turn the water hose on him. That means he gets showered every night, before Jammie time.
He is always good about standing (loose in the yard by the fence) without a halter to get showered down. I take his face mask off and have at it with the shower nozzle on the water hose.
Thursday night he was about 120' from the barn, grazing. I held up the water hose, called his name and asked if he wanted his bath. As I walked toward him with a 100' hose that wouldn't reach him, he surprised me by hurriedly walking to me, then past me and went right to his bath spot at the fence. I was still picking my jaw off the ground, when he turned his head to me, as if to say he was ready for his shower, what was I doing?
I have never tied any of my horses to bath them, but the horse in my avatar is the only other horse that would stand without a halter for a bath. I never expected my IR horse to walk 120' at liberty and assume his bath position without my help