Some of my tech school training was in classes titled Fluid Power (x), which pertained to hydraulics and pneumatics. We were told early hydraulic "fluid" was simply water.
Edit to add:
Makes me think of the words hydroforming and hydrant. The former uses hydraulic fluid and the latter is usually a water tap of some sort. Which flips the o and a usage.
Last edited by FiftySix; 11-07-19 at 03:55 PM.