I've never herd of adding apple juice
to a horses water before. I guess that's something new hehe :) .
I've always been told if my horses isnt drinking as much as it should in another arena to add Molasses.
They love it and can't resist. Also if you think you're horse is dehidrated grab the neck nere the whiter and get some skin and pull it back and then let go if it goes fast and stuff the horse is fine..