When is a Legionella Risk Assessment required?

The need for a Legionella risk assessment depends on the water systems present, how they are used, who may be exposed and who has control of the premises. It is generally required where a business, employer, landlord or other duty holder has a reasonably foreseeable risk of exposure and must demonstrate that the risk has been identified and managed.

Workplace and commercial premises

Employers and people who control non-domestic premises should assess water systems that could support Legionella growth or release contaminated water droplets. This can include hot and cold water services, showers, taps, cooling systems, spa pools, humidifiers, sprinkler systems and other equipment that produces an aerosol. The assessment should cover both normal operation and reasonably foreseeable situations such as infrequently used outlets, vacant areas, shutdowns or maintenance work.

Premises where assessments are commonly relevant include offices, factories, hotels, schools, healthcare settings, care homes, leisure facilities, warehouses, laboratories and multi-occupancy buildings. The presence of a simple water system does not automatically remove the duty to consider Legionella; the appropriate approach depends on the system's design, condition, temperature control, usage and potential for stagnation.

Legal duties and guidance

The Health and Safety at Work etc. Act 1974 and the Control of Substances Hazardous to Health Regulations 2002 provide the main legal framework for managing Legionella risks in workplaces. The Health and Safety Executive's Approved Code of Practice L8, Legionnaires' disease: The control of legionella bacteria in water systems, explains how duty holders should identify and control the risk. HSG274 provides more detailed technical guidance for different types of water system.

Following an assessment, the duty holder should establish a written control scheme where appropriate. This normally sets out the control measures, monitoring requirements, remedial actions, responsibilities and records needed to demonstrate that the system is being managed. The risk assessment itself is not a substitute for ongoing control and monitoring.

Rented and residential properties

Landlords and property managers should consider Legionella as part of their wider duties to provide safe accommodation and manage water-related hazards. The risk may be lower in a small, well-used domestic system than in a large or complex building, but it can increase where there are shared hot and cold water systems, storage tanks, long pipe runs, low occupancy, unused outlets or facilities such as showers and spa pools. Particular care is appropriate where residents may be more susceptible to serious illness.

There is not a single assessment format that applies to every rented property. The responsible landlord should identify the relevant hazards, decide whether existing precautions are adequate and retain suitable evidence of the steps taken. A competent specialist may be appropriate where the installation is complex, the property contains shared systems or the duty holder cannot confidently evaluate the risks.

Who should be considered in the assessment?

The assessment should identify people who could be exposed, including employees, contractors, visitors, residents, patients, pupils, customers and members of the public. It should also consider people who may be particularly vulnerable, such as older people, those with underlying health conditions, smokers and individuals with weakened immune systems. Their presence may affect the level of control needed, even where the water system itself has not changed.

What circumstances require a new or revised assessment?

A new assessment or significant review is appropriate when:

• a building is newly occupied or a water system is installed, extended, altered or recommissioned;
• the use, occupancy or population of the premises changes;
• water outlets become little used, redundant or subject to prolonged stagnation;
• temperatures, disinfection arrangements, water quality or monitoring results indicate a control problem;
• maintenance, refurbishment or changes to plant affect the system;
• a case or suspected case of Legionnaires' disease is associated with the premises;
• the existing assessment is based on outdated information or no longer reflects site conditions; or
• monitoring, inspection or audit identifies that controls are not being followed effectively.

A review is also necessary where the original assessment specifies a review date or where operational experience shows that the assumptions made in it are no longer reliable. The frequency should be proportionate to the system and risk rather than selected as an arbitrary calendar exercise.

What the assessment should establish

A suitable assessment should document the water systems and equipment, identify conditions that could allow Legionella to grow, consider routes of exposure and record the people who may be affected. It should then evaluate existing controls, assign responsibilities and set out further actions where necessary. Typical controls may include managing water temperatures, preventing stagnation, maintaining storage and distribution systems, cleaning relevant equipment and ensuring that monitoring and remedial procedures are followed.

Water testing can support an assessment or investigate a suspected control failure, but testing alone does not fulfil the duty to assess and manage the risk. Conversely, an assessment should not recommend routine sampling without explaining what the results will show and what action will follow. Sampling and analysis should be selected according to the system, the risk profile and the purpose of the investigation.

When specialist input is advisable

Specialist advice is particularly valuable for large, shared or technically complicated systems, premises with vulnerable occupants, buildings with a history of control failures and situations involving suspected exposure. The person carrying out the assessment should have sufficient knowledge, training and experience to understand the water system and the relevant Legionella controls. The duty holder remains responsible for ensuring that the assessment is suitable and that agreed actions are implemented.

For a business or property manager, the practical test is whether the water systems, occupants and control arrangements have been properly examined and whether the evidence remains current. Where that cannot be demonstrated, a competent Legionella risk assessment is an appropriate next step.