Symbol Ψ. A measure of the energy available in an aqueous solution to cause the migration of water molecules across *semipermeable membranes
during osmosis. Values of water potential cannot be calculated absolutely but are highest in pure water, which for convenience is given the value zero, and fall with increasing solute concentration. Water always tends to move from areas of high (less negative) to areas of low (more negative) potential. This principle governs water conduction in plants. Water potential is the sum of *osmotic potential
, *pressure potential
, and *matric potential
. The term is replacing the concept of *osmotic pressure
and differs from osmotic pressure in taking capillary and imbibitional forces into account.