eli5: If water is non-compressible, then why not use it in hydraulic machines instead of hydraulic oil?

Question

eli5: If water is non-compressible, then why not use it in hydraulic machines instead of hydraulic oil?

In: 1817

Answer 1

A lot of London was powered by high pressure water mains. Tower bridge was powered that way. As a child I was taken to see the steam engines presurising the system. Now the same hydraulic actuators in the bridge are fed with pressurised oil.