Water potential is the
potential energy of
water per unit volume relative to pure water in reference conditions. Water potential quantifies the tendency of water to move from one area to another due to
osmosis,
gravity, mechanical
pressure, or matrix effects such as
capillary action (which is caused by
surface tension). Water potential has proved especially useful in understanding water movement within
plants,
animals, and
soil. Water potential is typically expressed in potential energy per unit volume and very often is represented by the
Greek letter .