What is the bleach to water ratio for disinfection?

• A. 1 part bleach, 9 parts water
• B. 9 parts bleach, 1 part water
• C. 1 part water, 9 parts bleach
• D. 10 parts bleach, 0 parts water

Answer: (A)

Dilute bleach for disinfection by mixing one part bleach with nine parts water. This one-to-nine ratio yields a practical 0.5%–0.6% sodium hypochlorite solution that is strong enough to inactivate many pathogens on hard, nonporous surfaces while staying safer for surfaces and skin than using straight bleach. It provides the right balance between effectiveness and safety, requiring only brief contact on surfaces (follow the recommended contact time) before rinsing or allowing to air dry. Using more concentrated bleach (or pure bleach) is unnecessarily harsh and can damage surfaces or irritate skin, which is why the other options aren’t appropriate for routine disinfection.