This is something that I've been battling on and off for three years.
My youngest horse absolutely LOVES water... when it's in a pond, creek, river, stream, or lake. This same horse can NOT stand water when it comes from a hosepipe or spray-bottle.
When he was a foal, I tried to teach him that it was ok. He reared up, nearly went over backwards, fought, tried to get away... so much that I quit. His first year I gave him a bath with huge sponges and he still fought me, even though he tolerated it some. I tried again with the spray bottle last year a few times, but every time he went nuts. The last bath he got because he really needed it... I ended up tieing him a few inches away from a tree with a rope shipping halter and gave him a very quick bath. He still stretched the rope halter out about six inches fightig me and trying to get away. He's pretty much ok with water being poured from the hose onto his legs from the knee down, but if I go any higher he panics. He loves for me to hold the hose in front of his face so he can play with the water, though.
I was talking to my friend about his aversion to being wetted down with a hose or spray-bottle and she told me that one of her horses had the same problem. She ended up and got a spray bottle and her and her horse went in circles for about two hours with her spraying just one leg until the horse stood still. However, the horse of hers that she did this with is a 13.2 hand Welsh Pony... not an almost 15.2 hand Tennessee Walker. Also, while my friend is shorter than me, she is bigger than me and could hold onto her Pony mare a little easier than I could hold onto my gelding, I think.
I'm at my last rope... I'm seriously thinking about trying her method, but I don't want to get hurt... Is there any other safer ways to teach my boy to tolerate it? My mare just loves baths and being hosed down and doesn't mind sprays at all. I got her when she was 7, though, and she already enjoyed the water... so I didn't have to do anything more than reteach her how to stand tied without trying to pull whatever she was tied to across the yard/out of the ground... Lol.