Langelier Saturation Index

LSI and a corrosive/balanced/scaling interpretation from pH, temperature, calcium hardness, total alkalinity, and TDS.

Run the calculator

Example

You enter

pH 7.5
Water temperature 25
Temp unit C
Calcium hardness (mg/L CaCO3) 200
Total alkalinity (mg/L CaCO3) 150
TDS (mg/L) 320

You get

LSI 0.04
Saturation pH (pHs) 7.46

Details, formula, and sources

LSI = pH - pHs; pHs = (9.3 + A + B) - (C + D), with A = (log10(TDS)-1)/10, B = -13.12*log10(T_K)+34.55, C = log10(Ca)-0.4, D = log10(alkalinity).

Langelier (1936) saturation index as standardized in Standard Methods for the Examination of Water and Wastewater (APHA/AWWA/WEF) and AWWA practice, by name.

Method cited, not reproduced; the user supplies measured water-quality values.

Estimate. AHJ and licensed professional govern.

Field names used by the API: ph, temp, temp_unit, ca_mgl, alk_mgl, tds_mgl, lsi, phs

Temperature unit converted to Kelvin internallyLangelier equation