UV not effective in turbid water is a true statement. Which option best reflects this?

• A. True
• B. False
• C. Sometimes
• D. It depends

Answer: (A)

UV disinfection effectiveness hinges on UV light reaching microorganisms to inactivate them. Turbidity, or how cloudy the water is due to suspended solids, reduces this effectiveness because particles absorb and scatter UV energy, shielding microbes from the dose they need. When UV light is blocked or scattered, the actual dose delivered to pathogens drops, making disinfection less reliable in turbid water. To achieve reliable results, water should be clear enough (low turbidity and sufficient UV transmittance), often requiring pre-treatment to reduce turbidity. In practice, this means UV is much less effective as turbidity increases, so the statement reflecting that is true.