One of my horses does the same thing. He won't stand still for baths and he snorts at the hose. My mom suggested it was the sound of the hose so what I have to do is to start by barely spraying any water and then slowly start spraying more and more. It'll take some time but it'll get them used to it. Hope that helped!
Honestly, I've had my horse for 5 years and she is the same way. I show so she gets bathed every week. Still hates it. So recently I put a hay bag up for her to nibble on while I bathe and SHE STANDS! Crazy but maybe give it a try!