How do you calculate langlier index?

The Langelier Index (LI) is calculated using the formula LI = pH - pHs, where pH is the measured pH of the water and pHs is the saturation pH, which can be determined using the temperature and total dissolved solids (TDS) of the water. The saturation pH can be found using tables or specific equations that consider factors like calcium and alkalinity. A positive LI indicates that water is supersaturated with calcium carbonate and may lead to scale formation, while a negative LI suggests that the water is undersaturated and may corrode pipes.