A measure of the degree of saturation of calcium carbonate in water that is based on pH, alkalinity, and hardness. If the Langelier Index is negative, the water is corrosive (pH value below 7 or acidic). If the Langelier Index is positive, calcium carbonate can precipitate out of solution to form scale (pH value above 7 or basic). The Langelier Index will vary for cold water and for warm water.