Scaling of a reverse osmosis membrane may occur when sparingly soluble salts are concentrated within the element beyond their solubility limit. In a RO system the most common sparingly soluble salts encountered are CaSO4, CaCO3 and silica. Other salts (especially in sea water) creating a potential scaling problem are CaF2, BaSO4 and SrSO4. Anti-scalants (scale inhibitors) are used to preventing the fouling of RO membrane elements due to the formation of scale. The anti-scalants inhibit the nucleation step of salts in the concentrate of RO system and so delay crystal and precipitate occurrence.