The process of regulating water potential in order to keep fluid and electrolyte balance within a cell or organism relative to the surrounding.
In biology, osmoregulation is important to organisms to keep a constant, optimal osmotic pressure within the body or cell. It is the way by which an organism maintains suitable concentration of solutes and amount of water in the body fluids. An example employed by organisms is excretion (such as getting rid of metabolic wastes and other substances toxic to the body when they are in large amounts).
See also: osmosis, solute
Reference: animal and plant water regulation tutorial pages for related information in regards to evolutionary adaptations regarding osmoregulation.