The value of hydrostatic pressure for a fixed height column of fluid is directly proportional to the gravitional strength at a particular geographical location.
Generally if the height above sea level is increased the hydrostatic pressure will decrease. Also since the world is wider at the equator than the poles the gravitional pull will increase as you move closer to either the north or south pole.
For example, the acceleration due to gravity in Bangkok, Thailand is 9.783 m/s², whereas in London, England it is 9.812m/s². This represents a difference of approx 0.3%, therefore a column of water that has a hydrostatic pressure of 1000 mmWG in Bangkok will measure 1003 mmH20 in London, England even though the water level has not changed between the two locations.
In order to standardise the measurement of hydrostatic pressure the universal value for Earth’s gravity of 9.80665 m/s² is used.
This local gravity calculator will provide you with a good approximation of the local gravity at your location.