[halifaxbeard]

The hygroscopic nature of hydraulic fluid is there for the same reason it is in car brake fluid-

it's better to evenly distribute water throughout the fluid, than to have it accumulate in a low point

[Bjartr]

That's actually a really cool way to deal with that problem!

[mrguyorama]

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.