    # Langelier Index Calculation

As an example, suppose the drinking water supplied to animals has the following analysis. The LSI index is calculated at two temperatures: 25oC (room temperature) and 82oC (cage wash cycle). The colder incoming water will warm to room temperature in the manifolds. Residual water in the rack manifold can be heated to 82oC when the rack is in the cage washer.

• Water Analysis:

• pH = 7.5

• TDS = 320 mg/L

• Calcium = 150 mg/L (or ppm) as CaCO3

• Alkalinity = 34 mg/L (or ppm) as CaCO3

• LSI Formula:

• LSI = pH - pHs

• pHs = (9.3 + A + B) - (C + D) where:

• A = (Log10[TDS] - 1)/10 = 0.15

• B = -13.12 x Log10(oC + 273) + 34.55 = 2.09 at 25°C and 1.09 at 82°C

• C = Log10[Ca2+ as CaCO3] - 0.4 = 1.78

• D = Log10[alkalinity as CaCO3] = 1.53

• Calculation at 25oC:

• pHs = (9.3 + 0.15 + 2.09) - (1.78 + 1.53) = 8.2

• LSI = 7.5 - 8.2 = - 0.7

• Hence No Tendency to Scale

• Calculation at 82oC:

• pHs = (9.3 + 0.15 + 1.09) - (1.78 + 1.53) = 7.2

• LSI = 7.5 - 7.2 = + 0.3

• Hence Slight Tendency to Scale

### Consult the Water Glossary, Water Cooling Towers 