Environmental health: ultraviolet disinfection of water: practice question

A PSM question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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PSM · Environmental health: ultraviolet disinfection of water

Sample item

A hospital uses an ultraviolet unit to disinfect its drinking water. Which limitation of this method must be remembered?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. It leaves no residual disinfectant in the water

Ultraviolet light inactivates microorganisms by damaging nucleic acids and adds no taste or odour. However, it leaves no residual protection, so water can be recontaminated in storage or pipes, and it works poorly in turbid water that shields organisms.

Option by option

  • A. It imparts a strong taste to the water

    UV adds no taste or odour to water.

  • B. It leaves no residual disinfectant in the water (correct)

    Correct. UV treatment has no residual effect.

  • C. It cannot inactivate bacteria at all

    UV is effective in inactivating bacteria and many viruses.

  • D. It works best in highly turbid water

    Turbidity shields organisms from the light and reduces effectiveness.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

More PSM questions

Questions about this PSM question

What is the answer to this PSM question?

The best answer is B, It leaves no residual disinfectant in the water. Ultraviolet light inactivates microorganisms by damaging nucleic acids and adds no taste or odour.

Why is "It imparts a strong taste to the water" not the answer?

UV adds no taste or odour to water.

Why is "It cannot inactivate bacteria at all" not the answer?

UV is effective in inactivating bacteria and many viruses.

Why is "It works best in highly turbid water" not the answer?

Turbidity shields organisms from the light and reduces effectiveness.

What concept does this question test?

It tests Environmental health: ultraviolet disinfection of water in PSM. However, it leaves no residual protection, so water can be recontaminated in storage or pipes, and it works poorly in turbid water that shields organisms.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Environmental health: ultraviolet disinfection of water?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.