Water tools
Langelier Saturation Index (LSI) calculator
Estimate whether cooling, boiler, or process water will scale or corrode. Enter pH, temperature, TDS, calcium hardness, and alkalinity to get the LSI and its interpretation.
Tends to deposit a protective-to-problematic CaCO3 film. Watch scaling.
How it works
The Langelier Saturation Index compares the water's actual pH with the pH at which it is just saturated with calcium carbonate (pHs): LSI = pH − pHs.
pHs = (9.3 + A + B) − (C + D), where A = (log₁₀(TDS) − 1) / 10, B = −13.12 × log₁₀(°C + 273.15) + 34.55, C = log₁₀(Ca hardness as CaCO₃) − 0.4, and D = log₁₀(total alkalinity as CaCO₃). Calcium hardness and alkalinity are entered as mg/L of CaCO₃.
Positive LSImeans the water is scale-forming (CaCO₃ deposits); negative LSImeans it is corrosive (undersaturated, dissolving CaCO₃); near zero is balanced. The index is a tendency, not a rate, and does not account for phosphate, silica, or other scales.
Source: Langelier (1936); standard formulation as used across cooling-water and corrosion-control practice.
Related reading
These calculators use standard published formulas and are provided for preliminary engineering guidance. Confirm against measured data and vendor projections before design. Model your full water matrix in Nepti or post your project to compare provider proposals.