It is. Right up until you go to hit your brakes hard and it all boils out and removes your ability to apply brake pressure in an emergency and you had no idea how much water was in your line because there's no easy way to check, like a low spot with a sight glass.
Or if you leave a barrel of hydraulic fluid outside until it is partially water and it's not easy to notice when you are handling it.
Or if you leave a barrel of hydraulic fluid outside until it is partially water and it's not easy to notice when you are handling it.