When calcium hypochlorite is used for disinfecting a water supply, which method describes the recommended approach?

• A. dissolved in water as a dry chemical then injected into the water system
• B. dissolved in water as a dry chemical, allow to settle and the supernatant siphoned off and fed into the water system
• C. fed as a dry chemical directly into the pipeline
• D. dissolved in water, allow to settle, and the supernatant siphoned off and fed into the water system

Answer: (B)

When using calcium hypochlorite for disinfection, you want to deliver a clean, uniform disinfectant dose to the water. The proper approach is to dissolve the dry calcium hypochlorite in water to form a solution, then allow any undissolved solids to settle and siphon off the clear supernatant to feed into the water system. This ensures you’re introducing a consistent chlorine-containing solution rather than solids or slurry, which can clog equipment, cause uneven dosing, and lead to unreliable disinfection. By using the clarified solution, you achieve predictable residual chlorine levels throughout the distribution system while minimizing handling hazards.