Question 1

What is a good LSI for drinking water?

Accepted Answer

Slightly positive (0 to +0.3) is ideal under the EPA Lead and Copper Rule — enough to form a protective CaCO₃ film without causing scale problems.

Question 2

Is LSI the same as the Ryznar Stability Index?

Accepted Answer

No. RSI = 2 × pHs − pH and uses different stability bands (6.0–7.0 = balanced). LSI is simpler and more widely cited in US drinking water regs.

Question 3

Why does temperature matter?

Accepted Answer

CaCO₃ is less soluble in warm water, so the same pH and alkalinity are more scale-forming at 25 °C than at 5 °C. The B factor captures this.

Question 4

How do I raise LSI?

Accepted Answer

Increase pH (caustic, lime, soda ash), increase calcium (lime), or increase alkalinity (soda ash, sodium bicarbonate).

Langelier Saturation Index (LSI) Calculator – Corrosion & Scale