Legionella compliance requires organisations to assess risks, implement appropriate controls, and manage water systems effectively.
This guide explains the legal framework for legionella management, clarifies who is responsible, when testing may be required, and practical control measures to prevent legionella growth. We have also included temperature guidance, advice on responding to positive test results, and a practical compliance checklist to help review your current arrangements.
What is legionella compliance in the UK?
Legionella compliance is the legal requirement for UK employers, landlords, and building duty holders to identify, assess, and manage the risk of Legionella bacteria in man-made water systems.
The objective of legionella compliance is to prevent the growth and spread of Legionella bacteria that can cause Legionnaires’ disease, a serious and sometimes fatal form of pneumonia. To find out more, please read our guide, What is legionella, and how dangerous is it?
Under UK law, compliance is governed by:
- The Control of Substances Hazardous to Health (COSHH) Regulations 2002
- The Health and Safety at Work etc. Act 1974
- The Management of Health and Safety at Work Regulations 1999
- HSE Approved Code of Practice (ACOP) L8
- HSG274 Technical Guidance
These requirements are the foundation of legionella legislation and establish the framework organisations must follow.
What are the UK legionella regulations?
There is no single piece of legislation called the ‘UK Legionella Regulations’, but several legal duties combine to create the UK’s framework for legionella compliance.
Control of Substances Hazardous to Health (COSHH) Regulations 2002
The Control of Substances Hazardous to Health (COSHH) Regulations 2002 is the primary legal framework for managing legionella risks.
Legionella bacteria are classified as a biological agent under COSHH. Regulation 6 requires employers to carry out a suitable and sufficient assessment of the risks created by hazardous substances, including biological hazards such as legionella.
Where a risk is identified, Regulation 7 requires employers to prevent exposure where reasonably practicable or, where this is not possible, adequately control exposure through appropriate measures.
Health and Safety at Work etc. Act 1974
The Health and Safety at Work etc. Act 1974 (HSWA) forms the foundation of workplace health and safety law in the UK.
Under Section 2, employers have a duty to ensure, so far as is reasonably practicable, the health, safety, and welfare of their employees. Under Section 3, employers and self-employed people must also protect non-employees who may be affected by their activities, such as visitors, contractors, customers, residents, or members of the public.
In the context of legionella, these duties require organisations to manage water systems safely and take reasonable steps to prevent exposure to Legionella bacteria.
Management of Health and Safety at Work Regulations 1999
The Management of Health and Safety at Work Regulations 1999 build upon the duties established by the Health and Safety at Work etc. Act.
Under Regulation 3, employers must carry out a suitable and sufficient assessment of risks to employees and others who may be affected by their activities.
For legionella, this means conducting a legionella risk assessment to identify whether water systems could present a risk of exposure and evaluating the effectiveness of existing control measures.
The regulations also require employers to:
- Implement preventive and protective measures – Organisations must implement controls to prevent legionella growth and minimise the risk of exposure, such as temperature monitoring, flushing regimes, and system maintenance.
- Appoint competent persons to assist with health and safety compliance – Employers must appoint individuals with the knowledge, training, experience, and skills needed to help manage legionella risks effectively.
- Establish appropriate procedures – Clear procedures should be in place for assessing, monitoring, maintaining, and reviewing water systems.
- Provide information and training to employees – Employees with responsibilities for water systems should receive appropriate information and training. Legionella Awareness Training helps employees understand the risks, legal requirements, and control measures associated with legionella management.
ACOP L8
Legionnaires’ Disease: The Control of Legionella Bacteria in Water Systems (ACOP L8) is the Health and Safety Executive’s (HSE) Approved Code of Practice for legionella control.
Although ACOP L8 is not legislation, it has special legal status. Courts may regard compliance with ACOP L8 as evidence that an organisation has met its legal duties. Conversely, failure to follow this guidance may be used as evidence of non-compliance unless equivalent measures can be demonstrated.
ACOP L8 states the principles of legionella management, including:
- Identifying and assessing sources of risk – This involves examining water systems to identify conditions that could enable legionella bacteria to grow and spread.
- Appointing a duty holder with responsibility for legionella control – The duty holder is responsible for ensuring that legionella risks are managed effectively and that appropriate control measures are implemented.
- Implementing appropriate control measures – Control measures should be proportionate to the level of risk identified and tailored to the specific water system.
- Monitoring and reviewing control measures – Regular monitoring helps verify that controls remain effective and continue to manage risks adequately.
- Keeping records – Records provide evidence that legionella risks are being managed and legal duties are being met.
- Ensuring those involved are suitably competent – Individuals with legionella responsibilities should have the necessary knowledge, training, experience, and skills to carry out their duties effectively.
The document provides the framework that most organisations follow when developing their legionella compliance arrangements.
HSG274
HSG274 is the HSE’s detailed technical guidance that supports ACOP L8.
While ACOP L8 explains what organisations must achieve, HSG274 provides practical guidance on how to achieve it.
The guidance is divided into three parts:
HSG274 Part 1 – Evaporative Cooling Systems
Provides detailed guidance on managing cooling towers and evaporative condensers, including inspection, cleaning, water treatment, monitoring, and sampling requirements.
HSG274 Part 2 – Hot and Cold-Water Systems
Provides guidance for domestic and commercial hot and cold-water systems, including:
- Temperature control
- Water storage
- Calorifiers
- Pipework design
- Flushing regimes
- Monitoring and inspection frequencies
This is the section most used by employers, landlords, facilities managers, and property owners.
HSG274 Part 3 – Other Risk Systems
Provides guidance on managing other water systems that may present a legionella risk, including:
- Spa pools
- Vehicle wash systems
- Humidifiers
- Misting systems
- Ornamental fountains
Who is responsible for legionella compliance?
The person or organisation that has legal responsibility for the premises, water system, or activities giving rise to the risk is responsible for managing legionella risks. ACOP L8 refers to this person as the ‘duty holder’.
Depending on the type of premises, responsibility may fall to:
- Employers – where they control the premises and have responsibility for the health and safety of employees and others who may be affected by their activities.
- Building owners – where they retain responsibility for the maintenance and management of water systems.
- Facilities managers – where responsibility for managing building services has been delegated to them.
- Managing agents – where contractual arrangements place responsibility for maintenance and health and safety compliance on the agent.
- Landlords – where they have responsibility for water systems within rental properties.
- Company directors – particularly within smaller organisations where they retain overall responsibility for health and safety management.
Where legionella risk control responsibilities are shared between multiple parties, ACOP L8 recommends that duties are clearly defined and documented to avoid gaps in legionella management.
The duty holder may appoint a responsible person to oversee day-to-day legionella management, but overall accountability cannot be delegated. The responsible person should have sufficient authority, competence, and resources to ensure risk assessments are completed, control measures are implemented, monitoring is carried out, and records are maintained.
For larger or more complex premises, the duty holder may also appoint competent specialists, consultants, or water hygiene contractors to provide technical support, although legal responsibility for managing legionella risks remains with the duty holder.
What are legionella management and risk control measures?
Effective legionella management focuses on preventing the conditions that allow bacteria to multiply.
Common legionella risk control measures include:
Temperature management
Maintaining water temperatures outside the range in which Legionella bacteria thrive is one of the most effective control measures. Hot water should typically be stored at 60°C or above, while cold water should be kept below 20°C. Regular temperature monitoring can help identify issues before they become significant risks.
Preventing water stagnation
Legionella bacteria can multiply when water remains stagnant for prolonged periods. Water systems should be designed and maintained to encourage regular water movement and minimise areas where water can become trapped or unused.
Flushing little-used outlets
Taps, showers, and other outlets that are infrequently used can allow water to stagnate and increase the risk of bacterial growth. Regular flushing helps replace stagnant water with fresh water and supports the effectiveness of other control measures, such as temperature management.
Removing dead legs and redundant pipework
Dead legs are sections of pipework where water can become trapped and remain stagnant because there is little or no flow. Redundant pipework that is no longer required should be removed wherever possible, as it can provide an ideal environment for legionella bacteria to multiply.
Maintaining water storage tanks and associated equipment
Water storage tanks, calorifiers, shower heads, and other components should be inspected, cleaned, and maintained regularly. Effective maintenance helps prevent the build-up of scale, sludge, sediment, and biofilm, which can provide nutrients and protection for Legionella bacteria.
Monitoring system performance
Regular monitoring helps verify that control measures remain effective. This may include temperature checks, inspections, water quality monitoring, and reviews of maintenance activities. Any issues identified should be investigated and addressed promptly.
Maintaining accurate records
Records provide evidence that legionella risks are being managed appropriately and help demonstrate compliance with legal requirements. Records may include risk assessments, monitoring results, inspection reports, maintenance activities, corrective actions, and training records. ACOP L8 recommends retaining records for an appropriate period and ensuring they are readily available when required.
What temperature is safe for legionella?
Maintaining water temperatures outside the legionella growth range is one of the most effective legionella risk control measures available.
| Water system component | Target temperature | Requirement / guidance | Source |
| Hot water storage (calorifiers) | 60°C or above | Hot water should be stored at a minimum of 60°C. | HSE: Managing hot and cold water systems |
| Hot water outlets (taps and showers) | 50°C or above | Should reach 50°C within one minute of running (55°C in healthcare premises). | HSE: Managing hot and cold water systems |
| Cold water storage and outlets | Below 20°C | Cold water should be maintained below 20°C and achieve this temperature within two minutes at sentinel outlets. | HSE HSG274 Part 2: Hot and cold water systems |
| Legionella growth range | 20°C to 45°C | Temperatures within this range can support bacterial growth and multiplication. | HSE: What is Legionnaires’ disease? |
These temperatures are based on HSE guidance and represent commonly used control targets for hot and cold-water systems. Alternative control strategies may be appropriate where temperature control is not reasonably practicable, provided they achieve an equivalent level of risk control.
What are legionella water testing requirements for residential landlords?
According to the HSE’s guidance for landlords, the law does not require routine laboratory testing for legionella bacteria or the purchase of a Legionnaires’ testing certificate. Instead, landlords are expected to assess the risk of exposure to legionella and take appropriate steps to control that risk.
For most residential properties, effective control measures include maintaining appropriate hot and cold-water temperatures, preventing water stagnation, flushing little-used outlets and keeping water systems clean and in good condition.
What properties need legionella testing?
Legionella testing involves taking water samples and analysing them in a laboratory to determine whether legionella bacteria are present and, if so, at what concentration.
Legionella testing is generally reserved for higher-risk water systems where sampling forms part of a wider control strategy. This may include:
- Cooling towers and evaporative condensers – due to their potential to generate and disperse contaminated water droplets over a wide area.
- Spa pools and hot tubs – where warm water, aeration, and organic matter can create favourable conditions for bacterial growth.
- Hospitals and healthcare facilities – where occupants may be particularly vulnerable to infection.
- Care homes and supported living facilities – where residents may be older or have underlying health conditions.
- Large or complex hot and cold-water systems – particularly where there are multiple buildings, extensive pipework, or a history of control issues.
- Premises occupied by vulnerable individuals – such as healthcare settings or accommodation for people with weakened immune systems.
The need for legionella testing should always be determined by the findings of the risk assessment and the effectiveness of existing control measures. Routine testing is not automatically required simply because a building has a water system.
What should you do if legionella is detected in water?
If legionella is detected, the findings should be investigated and the effectiveness of existing control measures reviewed.
HSG274 recommends that the response should be proportionate to the level of contamination identified and the risks posed by the water system. The objective is to identify why Legionella bacteria have been able to proliferate and take appropriate corrective action.
Actions may include:
- Reviewing the risk assessment to determine whether it remains suitable and sufficient.
- Investigating the cause of the contamination, such as poor temperature control, water stagnation, inadequate maintenance, or ineffective water treatment.
- Reviewing monitoring records to identify trends or evidence of control failures.
- Cleaning and disinfecting the system where necessary.
- Improving control measures, such as temperature management, flushing regimes, or water treatment.
- Retesting the system, where appropriate, to verify that corrective actions have been effective.
- Updating records and management procedures to reflect the findings and actions taken.
In higher-risk environments, particularly where vulnerable people may be exposed, additional precautions are likely to be necessary until the risk has been adequately controlled.
Legionella compliance checklist: 5 essential steps
If an HSE inspector visits your premises, they will expect evidence that these five core compliance measures are in place.
1. Appoint a duty holder
Ensure responsibility for legionella management is clearly assigned to the person who controls the premises or water system.
2. Appoint a competent Responsible Person
Nominate a suitably trained and competent person to oversee day-to-day legionella management activities.
3. Complete a legionella risk assessment
Identify water systems, assess potential risks, and document the findings.
4. Review the risk assessment regularly
Review the assessment whenever there are significant changes to the water system, building use, occupancy, or control measures.
5. Implement appropriate control measures
Introduce controls proportionate to the risks identified, such as temperature management, flushing, maintenance, or water treatment.
6. Control water temperatures
Where temperature control is used, maintain hot water at appropriate temperatures and keep cold water below 20°C where reasonably practicable.
7. Prevent water stagnation
Remove dead legs, minimise redundant pipework, and ensure infrequently used outlets are managed appropriately.
8. Inspect, monitor, and maintain water systems
Carry out routine inspections, temperature checks, maintenance activities, and monitoring to confirm controls remain effective.
9. Train relevant employees
Provide Legionella Awareness Training to anyone with responsibilities for managing, maintaining, or monitoring water systems.
10. Keep records
Maintain records of risk assessments, monitoring results, inspections, maintenance, training, corrective actions, and reviews.
Strengthen your legionella compliance with training
Our Legionella Awareness Training provides employees, facilities managers, duty holders, responsible persons, and anyone involved in water system management with a practical understanding of legionella risks and how to control them.
The course covers legionella compliance, risk assessments, ACOP L8, control measures, monitoring requirements, and the responsibilities of those involved in managing water systems. Find out more about Legionella Awareness Training on our website, or call our friendly team today on 0203 011 4242 / [email protected]
Adam Clarke
Managing Director (Consulting)
