Conductivity is a measure of a materials ability to conduct electricity. It can be defined as a measure of electrical conduction, and it shows the ability of a material to pass a current. Conductivity can refer to different types of conductivity, including electrical conductivity, hydraulic conductivity, ionic conductivity, and thermal conductivity.

In the context of water, conductivity is a measure of the ability of water to pass an electrical current. This ability directly depends on the concentration of conductive ions in the water. Conductivity is useful as a general measure of water quality, and each water body tends to have a relatively constant range of conductivity that can be used as a baseline for comparison with regular conductivity measurements. Significant changes in conductivity could then be an indicator that a discharge or some other source of pollution has entered the aquatic resource.

The SI unit of conductivity is siemens per meter (S/m) ). Conductivity measurements are temperature-dependent, and many commercial systems offer automatic temperature correction). Despite the difficulty of theoretical interpretation, measured conductivity is a good indicator of the presence or absence of conductive ions in solution, and measurements are used extensively in many industries).