What is the Langelier Saturation Index?

 

The Langelier Saturation Index (LSI) is a measurement that shows the saturation level of calcium carbonate in water. It’s important because it helps predict if water will form scale or become corrosive. LSI calculation requires measurements of your water’s pH, alkalinity, calcium concentration, total dissolved solids, and temperature. These factors determine how “balanced” your water is. It’s often referred to as how “balanced” your water is.

One of the most common applications for this will be in pool water where the LSI is often unbalanced.

The Langelier Saturation Index (LSI) and Langelier Index (LI) are the calculation and are used interchangeably.

How to read your Langelier Saturation Index

 

The Langelier Index is represented by a number that should ideally be between -1 and 1.

 

Negative LSI: A negative LSI indicates that your water is under-saturated with calcium carbonate, making it corrosive. Corrosive water can damage pipes, water pumps, and appliances, shortening their lifespan. It can also cause your water to leech chemicals from your pipes. For pool owners, overly corrosive water can dissolve cement in plaster or other pool surfaces.

 

Positive LSI: A positive LSI means your water is over-saturated with calcium carbonate, leading to scale deposits. Calcium carbonate scale can clog pipes, reduce appliance efficiency, and leave unsightly white streaks on surfaces.

 

Balanced LSI: A Langelier Index near zero (between -1 and 1) is considered balanced. In this range, your water is less likely to cause corrosion or deposit excess scale.

 

How to Test for LSI

 

Since LSI is a calculation, you’ll need accurate values for each variable: pH, alkalinity, calcium concentration, total dissolved solids, and temperature.

 

To see the full LSI formula, you can check out this reference: https://www.gov.nl.ca/ecc/files/waterres-quality-drinkingwater-pdf-calculation-langelier-index.pdf

 

The most reliable way to measure your Langelier Index is through laboratory testing. With our Premium In-Lab Test Kit, you’ll receive accurate LSI results along with 49 other parameters analyzed in our EPA-certified lab.

 

Order your Premium In-Lab Test Kit Here

 

How to adjust your Langelier Saturation Index

 

• If Your LSI is Negative (Corrosive): Increase the hardness of your water to reduce corrosiveness. Many commercial products are available to boost water hardness, particularly for pools. Once you know your water’s profile, online calculators can help determine the exact amount of hardener needed.

• If Your LSI is Positive (Prone to Scaling): You can install a water softener to lower the LSI. Softened water reduces calcium hardness without significantly affecting pH.

 

Alternatively, in pools you can lower total alkalinity by adding muriatic acid. Pool supply stores typically carry muriatic acid and can advise on proper dosing.