Is there residual with UV?

• A. Yes
• B. No
• C. Sometimes
• D. Not applicable

Answer: (B)

With UV disinfection, there is no residual disinfectant in the water. UV light inactivates microorganisms as the water passes through the reactor, but it doesn’t add any chemical that remains in the effluent. Because there’s no residual germicidal agent, disinfection protection ends once the water exits the UV unit. If the water sits or is stored, microbes could potentially regrow since nothing chemical is left to continue disinfection. This contrasts with chemical disinfectants like chlorine, which leave a measurable residual.