Question

How is hydrostatic pressure created?

Answer 1

It is the pressure exerted by a non-moving (static) column of water (hydro).

Explanation:

Liquid water is an incompressible fluid, so a change in height exerts a change in pressure at the base of the fluid. This has significant implications for systems like hydraulics.

In the atmospheric pressure use it is a convenient and stable reference point. Using an inverted tube partially filled with water, with its opening submerged in a water reservoir, the variations in atmospheric pressures can be measured.

The atmosphere is composed of gases, which are compressible and can have very dynamic pressure changes. The use of the hydrostatic pressure measurement gives us a way to accurately measure and record those changes.

A change in the atmospheric pressure over the hydrostatic reservoir causes a change in the water column height in the tube. The actual pressure can be calculated from the mass of the water and the area of the tube.

For specific calculations, see:
http://www.engineeringtoolbox.com/hydrostatic-pressure-water-d_1632.html