The Langelier Index is an approximate indicator of the degree of saturation of calcium carbonate in water. It is sometimes referred to as the Langelier Saturation Index. In the calculation, it is the difference between the actual pH and a calculated pH.
The Langelier Index is an important characteristic in a potable water system:
- If the Langelier Index is negative (less than -1), the water is under-saturated with calcium carbonate and will tend to be corrosive in the distribution system
- If the Langelier Index is positive (more than +1), the water is over-saturated with calcium carbonate and will tend to deposit calcium carbonate scale in the distribution system.
- Preferred when the Langelier Index is close to zero (-1 to +1), where the water is neither corrosive nor scale forming
The Langelier Index is calculated using pH, alkalinity, calcium concentration, total dissolved solids and water temperature.
Calculations of the Langelier Index