LANGELIER SATURATION INDEX

An index (SI) based upon the pH of saturation of calcium carbonate; used to determine the tendencies of a water supply toward corrosion or scaling. A positive index indicates scaling tendencies; a negative one means corrosion tendencies. (Langlier Index = pH - pHs, where pH = actual pH of water and pHs = pH at which water having the same alkalinity and calcium content is just saturated with calcium carbonate.