- What is the Langelier Saturation Index (LSI)?
- The Langelier Saturation Index (LSI) measures the calcium carbonate scaling or corrosion tendency of water. It is the difference between the measured pH and the saturation pH (pHs): LSI = pH − pHs. A positive LSI means the water tends to deposit calcium carbonate scale, a negative LSI means it tends to be corrosive, and an LSI near zero is balanced.
- What LSI value indicates scaling versus corrosion?
- A positive LSI (greater than 0) indicates a scaling tendency, a negative LSI (less than 0) indicates a corrosive tendency, and an LSI of about 0 means the water is chemically balanced — neither scaling nor corrosive.
- How do the RSI and PSI differ from the LSI?
- The Ryznar Stability Index (RSI = 2·pHs − pH) and Puckorius Scaling Index (PSI = 2·pHs − pHeq) are always-positive scales that disambiguate borderline LSI readings. An RSI below about 6 trends toward scaling and above about 7 toward corrosion. The PSI substitutes an equilibrium pH for the measured pH, giving a better scaling prediction in poorly buffered water.
- What is saturation pH (pHs)?
- Saturation pH (pHs) is the pH at which water is exactly saturated with calcium carbonate — neither scaling nor corrosive. It is calculated from conductivity (converted to total dissolved solids), calcium hardness, total alkalinity, and temperature, and is the shared baseline for the LSI, RSI, and PSI indices.