Waterholes depends on circumstances :
What game are you hunting at the waterhole how are you hunting them rifle or bow.

If bow then yes it is ethical fro Africa couple of guys have stalked and has been succesfull but trophy wise it hasn't been that great the guys did it to see if they can.
So bowhunting I would say ethical.

With rifle I would and I have shot warthogs anytime. and will do it again.