Understanding the Threat of Legionella

Legionella bacteria occur naturally in water but can become dangerous when they multiply in man-made systems such as tanks, pipework, cooling towers and showers. When water droplets containing the bacteria are inhaled, they can cause Legionnaires’ disease, a serious form of pneumonia that can be fatal, particularly for vulnerable individuals.

For employers, landlords and duty holders, preventing exposure is not optional. It is a legal requirement under the Health and Safety at Work etc. Act 1974 and guided by the HSE’s Approved Code of Practice L8, known universally as ACoP L8.

What a Legionella Risk Assessment Involves

A Legionella Risk Assessment forms the foundation of every effective water safety strategy. It identifies where risks exist within a building’s water systems and outlines the measures needed to control them. A comprehensive assessment includes:

• A full review of the building’s water system layout
• Identification of potential sources of aerosol generation
• Temperature profiling of hot and cold water systems
• Examination of plant, equipment and stored water
• Assessment of maintenance practices and historical records
• Recommendations to control, reduce or eliminate identified risks

The assessment should be carried out by someone with suitable competence, as recognised in BS 8580-1:2019, which sets the standard for Legionella risk assessment methodology in the United Kingdom.

Why It Is Critical for Compliance

The HSE’s ACoP L8 places specific duties on those responsible for buildings, including the requirement to appoint competent persons, keep accurate records and regularly review assessments. Failure to comply can result in enforcement notices, prosecution and reputational damage.

A robust Legionella Risk Assessment helps duty holders demonstrate due diligence by providing clear evidence that risks have been identified, documented and managed appropriately.

Sectors Where Risk Is Highest

Although all buildings with water systems require an assessment, several sectors face heightened risks due to system complexity or vulnerable occupants. These include:

• Hospitals and healthcare settings
• Residential care homes
• Schools, universities and nurseries
• Hotels, leisure centres and spas
• Office buildings and large commercial premises

In these environments, maintaining safe water systems is essential for both legal compliance and the protection of service users, staff and visitors.

Common Issues Identified in Assessments

Even well-managed buildings can unknowingly harbour risk factors. Common issues revealed during professional assessments include:

• Inadequate temperature control due to system design or poor circulation
• Dead legs or redundant pipework encouraging stagnation
• Poorly insulated vessels or tanks
• Incomplete or inaccurate maintenance records
• Insufficient staff training on monitoring and flushing routines

Addressing these issues promptly reduces the likelihood of bacterial growth and strengthens an organisation’s compliance position.

The Role of Professional Expertise

While some organisations attempt to carry out their own assessments, the technical nature of water systems means that expert input is often essential. Competent assessors provide a detailed understanding of system behaviour, water hygiene science and industry standards.

Independent specialists can also offer impartial guidance, conduct system reviews, and help develop tailored control schemes that align with both ACoP L8 and wider water safety frameworks.

Maintaining Safety After the Assessment

A Legionella Risk Assessment is not a one-off document. It should be reviewed regularly, especially when:

• Systems are modified
• Occupancy levels change
• Monitoring records show anomalies
• Industry guidance is updated

Ongoing monitoring, staff training and periodic independent audits all help ensure long-term compliance and safe operation.

Conclusion

A thorough Legionella Risk Assessment is central to preventing outbreaks, maintaining compliance and protecting building users. By understanding how risks arise and taking informed action to control them, organisations can create safer environments and demonstrate strong governance.