since this is a trail etiquette and Chumbawamba appears to be a new trail rider, I will point out a bit of water etiquette,
When you come to a water hole if there are other horses there drinking stop and wait your turn, even if your horse doesnt need water it is rude to pass or ride off while horses are still drinking. A horse in that group may need the water but get anxious and wanna leave if they see you race off.
So stop, wait your turn, let your horse drink or not, move on a few feet out of the way till the other horses are done, then head on up the trail.
How is this any different from passing slower riders on the trail (something you've said you'd do without hesitation)?
The horses you pass by have just as much chance of getting jiggy and anxious as those drinking.
IMO, it's every rider's responsibility to control their horse. If your horse won't stand when others come and go, then that's on you and not on everyone else.