A Legionnaires risk assessment is the foundation for effective Legionella management. It identifies conditions that could encourage Legionella growth, how people could be exposed, who may be most at risk and the measures needed to prevent exposure.
In this guide, we look at what a thorough Legionella bacteria risk assessment should cover, how controls are evaluated, when water testing may be appropriate, what to expect from the final report and the steps to take afterwards.
How could people be exposed to Legionella?
Legionnaires’ disease is usually contracted by inhaling small droplets of water (aerosols) containing Legionella bacteria. Exposure can occur when a water system or equipment produces contaminated droplets that are released into the surrounding air.
Potential sources of exposure include:
- Showers and spray taps that produce fine water droplets during normal use.
- Cooling towers and evaporative condensers that can release aerosols into the surrounding environment.
- Spa pools and hot tubs where water is agitated and aerosols are readily generated.
- Humidifiers and misting systems that deliberately disperse water into the air.
- Decorative fountains and water features where water is sprayed, agitated or recirculated.
- Vehicle and equipment washing systems, including pressure washers that create a fine spray.
- Other water systems and equipment capable of producing aerosols that people could inhale.
Exposure can also occur during activities such as cleaning, maintenance, servicing and recommissioning where water may be disturbed or dispersed.
What should a Legionella risk assessment identify?
A Legionella bacteria risk assessment should cover four areas:
1. Identify where Legionella bacteria could grow
Assess the water system and associated equipment to identify conditions that could encourage Legionella bacteria to multiply. This includes:
- Check water temperatures to identify areas where water may remain between 20°C and 45°C, a range in which Legionella can grow.
- Identify stored or recirculated water where conditions could support bacterial growth.
- Look for areas of stagnation, including little-used outlets, redundant pipework and dead legs.
- Check for scale, rust, sludge and biofilm that can provide nutrients and favourable conditions for bacteria.
- Review the design and condition of the system to identify features that could make effective water management more difficult.
2. Identify how people could be exposed
Assess where contaminated water droplets could be produced and inhaled, as this is the main route of exposure associated with Legionnaires’ disease. This includes:
- Identify aerosol-producing outlets and equipment, such as showers, spray taps, cooling towers and spa pools.
- Consider how frequently outlets are used, particularly where infrequent use could contribute to stagnation.
- Assess where aerosols could be dispersed and whether employees, residents, visitors or others could be exposed.
- Consider maintenance and cleaning activities that could increase the potential for exposure.
3. Identify who could be exposed
Consider everyone who could encounter contaminated aerosols and whether some people may be particularly susceptible to infection. This includes:
- Identify employees, residents, tenants, visitors and contractors who could be exposed.
- Consider people who may be more susceptible to Legionnaires’ disease, including older people and those with certain underlying health conditions or weakened immune systems (see, Who could be at greater risk from Legionnaires’ disease?’ below).
- Take account of how the premises are used, particularly in healthcare, care and other settings where more vulnerable people may be present.
- Consider the frequency and duration of potential exposure when evaluating the overall level of risk.
4. Check whether existing controls are effective
Review how Legionella risks are currently managed and confirm that appropriate controls are implemented and maintained. This includes:
- Check temperature controls and monitoring arrangements to confirm the water system is operating as intended.
- Review measures for managing stagnation, including arrangements for little-used outlets.
- Check inspection, cleaning and maintenance programmes for water systems and associated equipment.
- Review monitoring and maintenance records to confirm that required checks are being completed and actions followed up.
- Confirm responsibilities are clearly allocated and that those responsible for managing Legionella risks have the necessary competence.
Who could be at greater risk from Legionnaires’ disease?
The HSE explains that everyone is susceptible to Legionnaires’ disease, although some people have a greater likelihood of developing the disease.
Factors associated with increased risk include:
- Older age – risk increases with age, with the HSE identifying people over 45 as a higher-risk group.
- Smoking – smokers have an increased risk of developing Legionnaires’ disease.
- Heavy alcohol consumption – identified by the HSE as another factor associated with increased susceptibility.
- Respiratory disease – including chronic respiratory conditions and other lung disease.
- Kidney disease – people with chronic kidney disease are among the groups identified as being at higher risk.
- Heart disease and diabetes – both are recognised risk factors.
- A weakened or impaired immune system – including people whose immune response is reduced by an illness, medical condition or treatment.
- Existing illness – particularly where this may increase an individual’s susceptibility to infection.
The people using a building can influence the level of risk and controls required. This is particularly important in hospitals, healthcare facilities, care homes and some residential settings, where more susceptible people may be present.
Hotels, leisure facilities and spas also require careful assessment due to changing occupancy, little-used outlets and aerosol-producing systems such as showers and spa pools.
How does an assessor determine whether Legionella controls are effective?
An assessor will look for evidence that Legionella risks are being actively managed over time. This helps establish whether the precautions identified for the water system are being carried out consistently.
Evidence may include:
- Monitoring records – showing that required checks have been completed at the appropriate intervals and results recorded.
- Inspection and maintenance records – demonstrating that water systems and associated equipment are routinely inspected, serviced and maintained.
- Cleaning records – confirming that relevant equipment and outlets are cleaned and maintained at the required frequency.
- Remedial actions – showing how issues identified through monitoring, inspections or previous assessments have been addressed.
- Previous assessment findings – confirming whether recommendations have been completed and whether outstanding actions are being managed.
- Roles and responsibilities – demonstrating that responsibility for managing Legionella is clearly allocated to competent people.
- Management arrangements – showing how checks, actions and concerns are communicated, recorded and followed through.
- Training and competence – checking that employees with responsibilities for managing or monitoring Legionella risks have received suitable training and understand the procedures and control measures they are expected to follow.
Records demonstrate how the system has been managed between assessments and can highlight trends or recurring issues that require attention.
Does a Legionella bacteria risk assessment include water testing?
Water testing may be recommended as part of a Legionella risk assessment, but it is not routinely required for every water system.
Whether sampling is needed depends on the type of system, the risks identified and how effectively those risks are being controlled. Testing may be appropriate where:
- Monitoring indicates that controls may not be effective, and further investigation is needed.
- Water temperatures or other control measures are not being consistently maintained.
- There are concerns about the condition or management of the water system.
- A higher-risk or more complex water system requires microbiological monitoring.
- There is an outbreak or suspected case of Legionnaires’ disease that requires investigation.
Our separate guide explains when Legionella testing is required and the circumstances in which sampling may be appropriate.
What should you do after a risk assessment for Legionnaires’ disease?
Once you receive the Legionnaires’ assessment, the next step is to act on its findings and ensure Legionella risks continue to be effectively managed.
Depending on the risks identified, this may involve:
- Complete recommended remedial work – address physical issues identified by the assessor, such as modifications or repairs to the water system.
- Develop a written control scheme where required – document how identified Legionella risks will be controlled, including the measures to be taken and how they will be monitored.
- Make responsibilities clear – ensure everyone involved in managing the water system understands their role and has the competence and authority to carry it out.
- Provide appropriate training – make sure employees with Legionella responsibilities have the knowledge and competence to carry out their role, understand relevant control measures and know how to recognise and report potential issues.
- Communicate relevant findings – make sure employees, contractors and others responsible for water-system management understand any actions or precautions that affect their work.
- Check that improvements are effective – follow up completed actions to confirm they have addressed the identified risk and controls are working as intended.
- Keep the assessment accessible – ensure those responsible for Legionella management can refer to the findings when managing the system or considering future changes.
Where risks are identified, the Health and Safety Executive’s Approved Code of Practice (ACOP) L8, Legionnaires’ disease: The control of legionella bacteria in water systems, provides practical guidance on how duty holders can comply with health and safety law.
When should a Legionella risk assessment be reviewed?
A Legionella risk assessment should be reviewed regularly and whenever there is reason to believe it is no longer valid.
According to the HSE’s guidance on reviewing Legionella risk assessments, a review should be considered where there are changes that could affect the assessment.
These may include:
- Changes to the water system or its operation – modifications to pipework, storage tanks, outlets or operating temperatures could introduce new risks or affect existing controls.
- Changes to the use of the building – a change in purpose or working practices may alter how frequently water systems are used and who could be exposed.
- Significant changes in occupancy – increased, reduced or intermittent occupancy can affect water usage and increase the potential for stagnation in some parts of the system.
- New information about risks or control measures – updated guidance, industry knowledge or information about the water system may indicate that the existing assessment or controls need to be reconsidered.
- Changes to key personnel responsible for managing the system – responsibilities should be reviewed when people change roles or leave to ensure effective Legionella management continues.
- Evidence that existing controls are no longer effective – recurring problems or changes in system performance may indicate that current precautions need to be reviewed or strengthened.
- Results from monitoring or checks that indicate a problem – unexpected temperatures, poor water turnover or other unusual findings may signal that the level of risk has changed.
- A case of Legionnaires’ disease associated with the system – the assessment and control measures should be urgently reviewed to identify potential sources of exposure and any further action required.
The review should establish whether the assessment still reflects the premises and whether the arrangements for controlling Legionella remain effective.
Is a Legionella risk assessment mandatory for landlords?
Landlords have a legal duty to assess and control the risk of exposure to Legionella in properties they rent out. These responsibilities arise under the Health and Safety at Work etc. Act 1974 and the Control of Substances Hazardous to Health Regulations 2002 (COSHH).
Our Legionella risk assessment for landlords guide explains landlords’ responsibilities in more detail. You can also read our guide to UK Legionella compliance for landlords for more information about the legislation and duties that apply.
Help your team recognise and manage Legionella risks
Make sure employees and managers have the knowledge and confidence to recognise Legionella risks and understand their responsibilities with our Legionella Awareness Training.
Developed by experienced health and safety professionals, this 25-minute online course covers how Legionella bacteria grow and spread, who may be at greater risk, Legionella risk assessment, legal responsibilities and important control measures.
Find out more about Legionella Awareness Training on our website, or talk to our friendly team today on 0203 011 4242 / [email protected]
Adam Clarke
Managing Director (Consulting)
