Groundwater is subsurface water in porous strata within a zone of saturation. Aquifers are groundwater formations capable of furnishing an economical water supply. Those formations from which extractions cannot be made economically are called aquicludes.

Permeability indicates the ease with which water moves through a soil and determines whether a groundwater formation is an aquifer or aquiclude.

The rate of movement of groundwater is given by
Darcy’s law:

Q=KIA

where
Q =flow rate, gal/day (m3/day)

K= hydraulic conductivity, ft/day (m/day)

I =hydraulic gradient, ft/ft (m/m)

A =cross-sectional area, perpendicular to direction of flow, ft2 (m2)