What chemical solution is typically used as bleach for water disinfection?

• A. Sodium hypochlorite solution, typically about 5% available chlorine
• B. Calcium hypochlorite powder
• C. Chlorine gas
• D. Hydrogen peroxide

Answer: (A)

Bleach for water disinfection is typically a chlorine-based solution, with sodium hypochlorite as the common liquid form. This liquid bleach is sold at about 5% available chlorine and is easy to store, transport, and dose. When added to water, sodium hypochlorite forms hypochlorous acid, the active disinfectant that oxidizes microbial cells and inactivates pathogens. It also provides a residual disinfectant in the distribution system, helping prevent recontamination. Calcium hypochlorite powder is used to generate chlorine in solid form, but it is not a liquid solution itself. Chlorine gas is hazardous and not commonly used as a household “bleach,” and hydrogen peroxide is a different disinfectant with different use patterns. So, the standard bleach for water disinfection is sodium hypochlorite solution around 5% available chlorine.