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Water systems and legionella questions for the Plumbing (JIB) (PLUM) specialist test

6 free questions on Water systems and legionella, from section E. Specialist: Plumbing (JIB). Every question is original and explains why each option is right or wrong.

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Question 1

Medium ·Link to this question (question 1)

You are commissioning a hot water cylinder in an office block.

What temperature should hot water be stored at, to control legionella?

Choose one answer.

  1. A. Below 20°C
  2. B. At least 60°C
  3. C. About 40°C, to save energy
  4. D. About 30°C
Show the answer and explanation

Answer: B

  • A. Wrong: Wrong. Below 20°C is for cold water.
  • B. Right: Right. HSE says hot water should be stored at 60°C or more.
  • C. Wrong: Wrong. That is a temperature legionella can grow at.
  • D. Wrong: Wrong. That is far too low to control legionella.

Explanation

Store hot water at 60°C or more, and keep cold water below 20°C.

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Question 2

Harder ·Link to this question (question 2)

You are checking the hot taps in a building you have just plumbed.

What does HSE say the water should reach at the outlets?

Choose one answer.

  1. A. 40°C within 10 minutes
  2. B. 20°C within 1 minute
  3. C. 50°C within 1 minute
  4. D. 30°C within 5 minutes
Show the answer and explanation

Answer: C

  • A. Wrong: Wrong. That is too cool and too slow.
  • B. Wrong: Wrong. 20°C is the upper limit for cold water.
  • C. Right: Right. HSE says hot water should reach 50°C within 1 minute at the outlets (55°C in healthcare premises).
  • D. Wrong: Wrong. That is too cool and too slow.

Explanation

Hot water should reach 50°C at the outlets within 1 minute (55°C in healthcare).

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Question 3

Medium ·Link to this question (question 3)

You are running a cold water main through a warm plant room.

What temperature should cold water be kept at, where possible?

Choose one answer.

  1. A. Between 20°C and 45°C
  2. B. Exactly 37°C
  3. C. It doesn't matter for cold water
  4. D. Below 20°C
Show the answer and explanation

Answer: D

  • A. Wrong: Wrong. That is the range legionella likes.
  • B. Wrong: Wrong. That is close to body temperature and helps legionella grow.
  • C. Wrong: Wrong. Warm cold water lets legionella grow.
  • D. Right: Right. HSE says cold water systems should be kept below 20°C where possible.

Explanation

Keep cold water below 20°C, so pipes in warm places may need insulating.

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Question 4

Medium ·Link to this question (question 4)

A supervisor asks you to look for dead legs in an old system.

What is a dead leg?

Choose one answer.

  1. A. A pipe to an outlet that is rarely used
  2. B. A pipe that carries only waste water
  3. C. A pipe that has been lagged to stop it freezing
  4. D. A pipe with a frozen section
Show the answer and explanation

Answer: A

  • A. Right: Right. HSE describes a dead leg as a pipe to an outlet that water flows through, but the outlet is unused or rarely used. Water stagnates there.
  • B. Wrong: Wrong. That is a waste pipe.
  • C. Wrong: Wrong. Lagging doesn't make a dead leg.
  • D. Wrong: Wrong. A dead leg is about water that rarely moves.

Explanation

A dead leg is a pipe to an outlet that is rarely used, so the water in it stagnates.

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Question 5

Medium ·Link to this question (question 5)

You are fitting a shower in a care home, used by vulnerable residents.

What must be fitted to prevent scalding?

Choose one answer.

  1. A. A hotter boiler so water heats faster
  2. B. A Type 3 thermostatic mixing valve
  3. C. A bigger cylinder for more flow
  4. D. A sign asking residents to take care
Show the answer and explanation

Answer: B

  • A. Wrong: Wrong. That would make scalding more likely.
  • B. Right: Right. HSE says where vulnerable people use baths or showers, a TMV Type 3 must be fitted so water isn't delivered above 44°C.
  • C. Wrong: Wrong. That doesn't limit the temperature.
  • D. Wrong: Wrong. A sign isn't enough for vulnerable residents.

Explanation

Above 44°C water can scald. Where vulnerable people bathe, fit a Type 3 TMV.

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Question 6

Medium ·Link to this question (question 6)

During a long refurbishment, some taps are still needed but are hardly ever used.

What does HSE say?

Choose one answer.

  1. A. Cover the spouts with tape
  2. B. Turn the hot water down to save energy
  3. C. Flush them through regularly
  4. D. Leave them alone until handover
Show the answer and explanation

Answer: C

  • A. Wrong: Wrong. That doesn't stop water stagnating.
  • B. Wrong: Wrong. Lower temperatures help legionella grow.
  • C. Right: Right. HSE says outlets that are still needed but not regularly used should be flushed through regularly.
  • D. Wrong: Wrong. Stagnant water lets legionella grow.

Explanation

Flush rarely used outlets regularly, and drain systems that are no longer needed.

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