Langelier Saturation Index (LSI) Calculator
Determine if your water is corrosive, balanced, or scale-forming. Get treatment recommendations to protect your equipment and membranes.
LSI Result
Calculation Details
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Contact Our EngineersFrequently Asked Questions
What is the Langelier Saturation Index?
The LSI predicts whether water will tend to dissolve or deposit calcium carbonate. Calculated as LSI = pH - pHs. Negative values indicate corrosive water, zero is balanced, and positive values indicate scaling tendency.
What is the ideal LSI value for RO systems?
The concentrate stream LSI should be below +0.5 to prevent CaCO3 scaling on membranes. Above +1.0 indicates high risk. Antiscalant dosing or acid injection maintains safe levels.
How do you correct a negative LSI?
Raise pH with soda ash or caustic soda, increase alkalinity with sodium bicarbonate, or add calcium with lime. Corrosion inhibitors (polyphosphates, orthophosphates) also help in distribution systems.