An index reflecting the equilibrium pH of a water with respect to calcium and alkalinity; used in stabilizing water to control both corrosion and scale deposition. The Langelier index (LI) can be formulated as the difference between the real pH and the estimated pH of the water supply. LI provides a close and accurate number of the degree of overload of calcium carbonate in the water body. Experts utilize the total dissolved solids (TDS), pH, calcium concentration, and temperature of the water to ascertain the Langelier Index.