Which statement correctly describes the role of alkalinity in water treatment?

• A. pH affects reaction rates and disinfection
• B. Alkalinity buffers pH changes
• C. Hardness can cause scaling
• D. Alkalinity directly increases hardness

Answer: (B)

Alkalinity acts as a buffer in water treatment, resisting changes in pH. It comes mainly from carbonate and bicarbonate (and some hydroxide) ions that neutralize added acids or bases, keeping pH stable. This buffering is crucial because disinfectants and treatment processes work best within a certain pH range, and a stable pH helps protect pipes and minimize corrosion.

The other statements describe aspects of pH behavior or hardness, not what alkalinity does. pH itself influences reaction rates and disinfection, but that isn’t the buffering role of alkalinity. Hardness relates to calcium and magnesium and can cause scaling, which is not a direct function of alkalinity. Alkalinity does not directly increase hardness.