This was decades ago, our riding center owner would go to the slaughter plant and pick suitable prospects.
We received 15 feral horses right off the mountains every June and they were good school horses by September.
They came to our riding center packed like sardines seven or so on a truck with wooden sides, several grooms would reach over and put woven halters with a 4’ rope woven on them and a thick leather collar with a big D and big 4’ chain hanging from it.
Then the gate was opened and horses jumped off and were herded down the aisle each one to their own box stall.
The grooms trained to gentle them would work with them all day long, going in there with hay and grain and treats and teach them gently to give to pressure.
There was no water in the stalls, the riding center had troughs outside and horses were led several times a day to them for a drink.
Feral horses were first let out to follow an old horse, after they would lead they were led to water several times a day and worked outside the stalls a bit, etc.
Even the night watchman took them all out to drink a couple times a night.
Once they were far enough along, it took for most just a few days, the riding instructor would take over and lead one to a chain on the wall, work until he was sure they would tie safely, not pull back, grab a hose and start on their feet.
As I learned from him, he would get a gentle stream of water controlled by your finger how much spray or force on one foot as by accident and immediately move to another place, then another foot, the water would be hitting here and there too fast for the horse to keep track and if done right, horse would after a bit just stand there.
After a little of that water was directed a bit higher and higher and all over the horse, again keep it moving on the horse and off, always catch the horse before it moves, so it doesn’t think moving made the water go away.
After a bit of that, most horses you could be running water on them and slowly approach them and end up even stroking them, horses that before had not been handled until a few days ago, now were standing there and letting you almost pick a foot a little.
Most horses learned so fast, it was amazing.
If one was still hesitant, he would be brought up again that afternoon for a short review.
That water system was an intrinsic part of what the gentling protocol had been for years and it worked very well, in experienced hands.
Telling this story in case OP can apply any of this to her feral horse’s few quirks, especially the hose one.
It was amazing to watch them work with those scared horses.
I was 13 turning 14 and the test pilot once we started them under saddle.