Langelier Saturation Index
LSI and a corrosive/balanced/scaling interpretation from pH, temperature, calcium hardness, total alkalinity, and TDS.
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
Checked against published worked examples from: Langelier (1936) / Standard Methods (APHA/AWWA/WEF).
Details, formula, and sources
Formula or tableLSI = 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).
Source and editionLangelier (1936) saturation index as standardized in Standard Methods for the Examination of Water and Wastewater (APHA/AWWA/WEF) and AWWA practice, by name.
Free accessMethod cited, not reproduced; the user supplies measured water-quality values.
What governsEstimate. AHJ and licensed professional govern.
API field namesph, temp, temp_unit, ca_mgl, alk_mgl, tds_mgl, lsi, phs
- Temperature unit converted to Kelvin internallyLangelier equation