Water potential

From Glossary of Meteorology

water potential

The potential energy per unit mass of water with reference to pure water at zero potential.

The water potential τ is made up of several components,
where τg is the component due to gravity, τm is the matrix potential that arises from the attraction of the soil matrix for water and water molecules for each other, τp is the pressure potential that is the ratio of the hydrostatic or pneumatic pressure to the density of water, and τo is the osmotic potential that is a driving force for water movement when solute movement is restrained with a semipermeable membrane