What happens to chlorine’s disinfecting efficiency as water temperature rises?

• A. Decreases
• B. The same
• C. Increases
• D. Fluctuates

Answer: (C)

Chlorine disinfection is driven by chemical reaction rates, which speed up as temperature increases. When water warms up, molecular collisions between chlorine species and microbial cells become more frequent and energetic, speeding up the oxidation and damage to cellular components that inactivate microorganisms. Although higher temperature can reduce chlorine solubility a bit, the faster reaction rate typically leads to greater disinfection effectiveness, so the overall efficiency rises with rising water temperature. Therefore, the correct idea is that disinfection efficiency increases as temperature goes up.