Scale deposition is a difficulty encountered with water containing ions of sparingly soluble salts, notably calcium carbonate, calcium sulfate, magnesium hydroxide, calcium phosphate, and silica. The most important single factor determining the intensity of scaling is the supersaturation (SS) level of the deposit forming species. SS conditions are achieved when a solution is concentrated beyond the solubility limits of one or more of its constituents by water evaporation (as in water cooling towers) or by separation of pure water at ambient temperature (as in membrane processes). SS conditions can be also achieved by a change in temperature. A solution of an inverted solubility salt (such as CaCO3, Mg(OH)2, and CaSO4) in contact with a hot surface can attain SS by the inverted solubility effect and deposit scale on the hot surface, even when undersaturation conditions prevail in the bulk of the solution.