What scale prevention chemical can loosen existing deposits and cause red-water complaints?

• A. Silicates
• B. Sodium hexametaphosphate
• C. Carbon dioxide
• D. Sulfuric acid

Answer: (B)

Scale prevention chemicals that act as dispersants can break apart existing mineral deposits in the distribution system. Sodium hexametaphosphate is a polyphosphate used as a sequestering and dispersing agent: it binds calcium and magnesium to prevent new scale from forming, and at the same time helps loosen or suspend already accumulated deposits. When these deposits are disturbed, iron or other metals held in the scale can be released, leading to red-water complaints as the discolored water flows through the system.

The other options don’t fit this behavior. Silicates mainly form protective films and reduce corrosion rather than actively dispersing existing scale. Carbon dioxide is used to adjust carbonate chemistry and pH, not as a scale-dispersing inhibitor. Sulfuric acid changes pH and can dissolve some deposits, but it’s not a scale prevention chemical that deliberately loosens deposits and can cause red water in routine operation.