Prelims 2012 · archive
EasyWhat is the role of ultraviolet (UV) radiation in the water purification systems?
- 1.It inactivates/kills the harmful microorganisms in water.
- 2.It removes all the undesirable odours from the water.
- 3.It quickens the sedimentation of solid particles, removes turbidity and improves the clarity of water.
Which of the statements given above is/are correct?
Answer & explanation
Answer: (a) 1 only
UV radiation is a disinfectant. It damages the genetic material of microbes so they cannot multiply or infect. It is a purely physical treatment. It does not remove odours, and it does not settle or filter out particles. The water must already be clear for UV to work well. Only statement 1 is correct.
- ✓ 1. UV light disinfects water by inactivating harmful microorganisms such as bacteria, protozoa and viruses. This is the main reason UV units are fitted in water purifiers.
- ✗ 2. UV only inactivates microbes. Taste- and odour-causing compounds need other treatment, such as oxidation with chemical agents or activated carbon. The word 'all' also makes the claim too strong.
- ✗ 3. UV does not cause sedimentation or remove turbidity. Turbid water actually reduces UV efficiency, because particles shield microbes from the light. So water is filtered or settled before the UV stage.
- ✗ (c) This option is tempting because statement 1 is right. But statement 3 confuses disinfection with clarification (coagulation, sedimentation and filtration).
Remember · UV is only a disinfectant: it inactivates microbes and leaves no residual effect. It cannot remove turbidity, odour or dissolved impurities, so clear, pre-filtered water is needed.
Sources
- WHO – Evaluating household water treatment options: health-based targets and microbiological performance specifications (Annex 2, UV light technologies) ↗ “UV radiation has been used in drinking-water treatment for over 100 years (Ward, 1893; Baker, 1948), and its mechanisms for inactivating microbes have now been well characterized”
- Drinking Water Inspectorate (UK) – UV disinfection, private water supplies treatment guide ↗ “Pre-filtration provides an additional barrier to passage of oocysts into the treated water removes particles that shield microorganisms from the UV light”
- US EPA – Ultraviolet Disinfection Toolkit for drinking water systems ↗ “chemical disinfectants may be needed to oxidize other constituents present in the water (e.g., iron, manganese, or taste- and odor-causing compounds)”
Question: UPSC Civil Services (Preliminary) 2012, General Studies paper. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). ·