Which index can indicate whether water will be corrosive or deposit-forming?

• A. Langelier Saturation Index
• B. Alkalinity Index
• C. Calcium Hardness Index
• D. pH Stability Index

Answer: (A)

The Langelier Saturation Index (LSI) is a critical tool used in water treatment to determine the corrosive or deposit-forming tendencies of water. This index assesses the saturation state of calcium carbonate in water, which is an important factor in evaluating water's potential to either corrode pipes and equipment or to form scale deposits.

When the LSI is positive, it indicates that water is supersaturated with respect to calcium carbonate, suggesting it will tend to precipitate calcium carbonate and deposit it as scale. Conversely, a negative LSI indicates that the water is undersaturated with calcium carbonate, which means it has the potential to corrode metals and dissolve materials like piping and plumbing fixtures.

Each of the other indices serves important roles but does not directly indicate the balance between corrosion and scale formation. The Alkalinity Index is a measure of the water's ability to neutralize acids, while the Calcium Hardness Index quantifies calcium levels without indicating saturation potential. The pH Stability Index also plays a role in assessing water quality but does not specifically connect to calcium carbonate saturation in the same way that LSI does.

Using the LSI allows operators to make informed adjustments in treatment processes to mitigate corrosion or prevent unwanted scale formation, ensuring that both the water