Legionella risk management

Legionnaires disease is a potentially fatal pneumonia caused by legionella bacteria - infection is caused by breathing in small droplets of water contaminated by the bacteria.

To comply with Health and Safety Legislation we have put into place procedures to control the risk of legionella.

Equipment containing water has been risk assessed and control/maintenance procedures identified.  Please contact the Technical Support Team for more details.

Taps identified as ‘infrequently used’ in the Department of Biology will typically be managed by gently purging / running the tap for several minutes before use, with minimum aerosol production. 

Taps labelled ‘Out of use’ are disconnected and will require purging on reconnection before use.


All identified infrequently used taps are labelled:

'Infrequently Used Tap & Legionella Control: Run Gently to Drain for Several Minutes Before Use with Minimum Aerosol Production'   

  • Before using an ‘infrequently used tap’, users to gently run tap to drain for several minutes, whilst minimising any aerosol production (to attach piping to tap if considered necessary)

All unused taps are labelled :

'Legionella control: Out of Use'

  • Before use, a previously unused tap requires purging: Open the tap slowly at first with the minimum of spray (it may be necessary to use additional piping to ensure safe flow of water to the drain) allowing the water to run gently for several minutes before use

Please contact the Technical Support Team if you have any queries.

More details

Legionnaires' disease - information for staff.

Legionnaires' disease is a potentially fatal pneumonia caused by legionella bacteria. Other similar but less serious conditions caused by legionella bacteria include Pontiac Fever.

Infection is caused by breathing in small droplets of water contaminated by the bacteria. The disease cannot be passed from person to person. The incubation period is between 2-10 days (usually 3-6 days). Symptoms include high fever, chills, headache and muscle pain, dry cough and difficulty with breathing. Legionnaires disease can be treated with appropriate antibiotics.

Everyone is susceptible to infection but some people are at higher risk e.g. those over 45 years of age, smokers and heavy drinkers, those suffering from chronic respiratory or kidney disease, and people whose immune system is impaired.

Legionella bacteria are common and can be found naturally in environmental water sources such as rivers, lakes and reservoirs. They have been found in water temperatures of 6 - 60°C. Water temperatures of 20-45°C seem to favour growth. They do not appear to multiply below 20°C and above 60°C. They may, however, remain dormant in cool water and multiply only when water temperatures reach a suitable level. Temperatures may also influence virulence; legionella bacteria held at 37°C have greater virulence than the same legionella bacteria kept below 20°C. They are killed by temperatures greater than 60°C.

Legionella bacteria require nutrients to multiply - sources include commonly encountered organisms within the water system itself e.g. algae, amoeba and other bacteria. The presence of sediment, sludge, scale and other material within the system, together with biofilms (thin layers of micro-organisms which may form a slime on the surface in contact with water) also provide a role in harbouring and providing favourable conditions in which the legionella bacteria may grow.

A number of factors are required to create a risk of acquiring legionellosis such as:

  • The presence of legionella bacteria
  • Conditions suitable for multiplication e.g. 20-45°C and a source of nutrients
  • A means of creating and disseminating breathable droplets
  • Presence (and numbers) of people who maybe exposed, especially in premises where occupants are particularly vulnerable.

The HSC Approved Code of Practice states that a reasonably foreseeable risk of exposure to legionella bacteria exists in:

  • Water systems incorporating a cooling tower
  • Water systems incorporating an evaporative condenser
  • Hot and cold water systems
  • Other plant and systems containing water which is likely to exceed 20°C and which may release a spray or aerosol during operation or when being maintained.

In general, proliferation of legionella bacteria may be prevented by:

  • Avoiding water temp between 20°C and 45°C
  • Avoiding water stagnation which may encourage the growth of biofilm
  • Avoiding the use of materials in the system that can harbour or provide nutrients for bacteria
  • Keeping the system clean to avoid build up of sediments
  • The use of a suitable water treatment programme where it is appropriate and safe to do so
  • Ensuring that the system operates safely and correctly and is well maintained.

Employers must:

  • Identify and assess sources of risk – this includes checking whether conditions are present which will encourage bacteria to multiply e.g. is the water temp. 20-45°C; there is a means of creating and disseminating breathable droplets and if there are susceptible people who may be exposed to the contaminated aerosols
  • Prepare a scheme for preventing or controlling the risk
  • Implement, manage and monitor precautions
  • Keep records of the precautions
  • Appoint a person to be managerially responsible

Notes for personnel performing maintenance to prevent the proliferation of legionella bacteria

  • Understand why the maintenance is being performed (see above)
  • Understand the risks from legionella bacteria (see above)
  • Ensure that safety precautions are taken i.e. ensure that no aerosols are produced when cleaning equipment or when running infrequently used water outlets
  • Ensure that records are kept of the maintenance.

Further information:

The control of legionella bacteria in water systems. Approved Code of Practice and guidance. HSC – ISBN 0717617726