Understanding the Langelier Saturation Index (LSI)
The Langelier Saturation Index (LSI) is a key water chemistry tool used to predict whether water will cause scaling or corrosion in pipes and treatment systems. It measures the balance between pH, alkalinity, calcium hardness, total dissolved solids, and temperature to determine water stability. A positive LSI value indicates scaling potential (the tendency to form calcium carbonate deposits), while a negative LSI suggests corrosive water that can damage metal surfaces. Maintaining an LSI close to zero ensures water is in chemical equilibrium—neither scaling nor corrosive. Monitoring the Langelier Index helps improve water treatment efficiency, extend equipment life, and maintain safe, high-quality water in industrial, municipal, and household systems.
The name Langelier comes from Wilfred F. Langelier, an American chemist and professor of civil and sanitary engineering at the University of California, Berkeley.
He developed the Langelier Saturation Index (LSI) in 1936 as part of his pioneering research on water chemistry and corrosion control. His work helped engineers understand how pH, hardness, alkalinity, and temperature interact to influence whether water is scale-forming or corrosive. The index has since become a standard tool in water treatment, cooling tower management, and pipeline maintenance worldwide.
Before he was a professor changing the world of water science and sanitation, he was a chemist at the Illinois State Water Survey and a graduate student at the University of Illinois