Hydraulic head is a specific measurement of water pressure. It is usually measured as a water surface elevation, expressed in units of length, at the entrance of a piezometer.
In an aquifer, it can be calculated from the depth to water in a well, and given information of the well elevation and screen depth. Hydraulic head can similarly be measured in a column of water using a standpipe piezometer by measuring the height of the water surface in the tube relative to a common factor. The hydraulic head can be used to determine a hydraulic gradient between two or more points.
The static head of a pump is the maximum height it can deliver. The capability of the pump can be read from its Q-H curve (flow vs. height).
Head is equal to the fluid's energy per unit weight. Head is useful in specifying centrifugal pumps because their pumping characteristics tend to be independent of the fluid's density.