Groundwater discharge is the volumetric flow rate of groundwater through an aquifer.

Total groundwater discharge, as reported through a specified area, is similarly expressed as:

where

For example, this can be used to determine the flow rate of water flowing along a plane with known geometry.

The discharge potential is a potential in groundwater mechanics which links the physical properties, hydraulic head, with a mathematical formulation for the energy as a function of position. The discharge potential, ${\textstyle \Phi }$ [L³·T⁻¹], is defined in such way that its gradient equals the discharge vector.

${\displaystyle Q_{x}=-{\frac {\partial \Phi }{\partial x}}}$

${\displaystyle Q_{y}=-{\frac {\partial \Phi }{\partial y}}}$

Thus the hydraulic head may be calculated in terms of the discharge potential, for confined flow as