Enter the actual pH and the saturation pH of the water into the calculator to determine the Langelier Saturation Index. This calculator can also evaluate any of the variables given the others are known.

## Langelier Saturation Index Formula

The following formula is used to calculate the Langelier Saturation Index (LSI).

LSI = pH - (pHs)

Variables:

• LSI is the Langelier Saturation Index
• pH is the actual pH of the water
• pHs is the saturation pH of the water

To calculate the Langelier Saturation Index, subtract the saturation pH of the water from the actual pH of the water. The result is the Langelier Saturation Index, which indicates the water’s tendency to precipitate or dissolve scale. A positive LSI indicates a tendency to precipitate scale, while a negative LSI indicates a tendency to dissolve scale.

## What is a Langelier Saturation Index?

The Langelier Saturation Index (LSI) is a calculated number used to predict the calcium carbonate stability of water. It indicates whether the water will precipitate, dissolve, or be in equilibrium with calcium carbonate. LSI is used in the water treatment process to manage the scaling and corrosion tendencies of water. A positive LSI indicates the water is supersaturated and has a tendency to form scale, while a negative LSI indicates the water is undersaturated and has a tendency to dissolve existing scale.

## How to Calculate Langelier Saturation Index?

The following steps outline how to calculate the Langelier Saturation Index (LSI).

1. First, determine the actual pH of the water (pH).
2. Next, determine the saturation pH of the water (pHs).
3. Next, gather the formula from above = LSI = pH – pHs.
4. Finally, calculate the Langelier Saturation Index.
5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

actual pH of the water (pH) = 7.5

saturation pH of the water (pHs) = 7.2