When people think about Legionella control, they often associate it with settings such as hospitals, care homes, hotels, or large commercial buildings.
However, the construction industry has its own set of legal responsibilities, and these obligations begin much earlier in the process, long before a building is handed over or even occupied.
In fact, compliance with Legionella regulations starts at the design stage, and failing to address it early on can lead to long-term safety risks, costly remediation work, and potential legal consequences.
This blog will break down the core legal responsibilities in the construction industry and explain why conducting a Legionella risk assessment during the design phase is essential for creating compliant, safe water systems.
Why Construction Projects Must Consider Legionella Early
Water systems that are installed during construction can create ideal conditions for Legionella growth if they are not designed, installed, and commissioned correctly. Common issues that are often seen on construction sites include:
- Pipework left stagnant for weeks at a time
- Temporary water supplies with minimal temperature control
- Poorly insulated or oversized pipework
- Dead legs created during rushed installations
- Systems that are left unflushed or uncommissioned
These issues can be inadvertently built into the water system before anyone realizes they exist, and by the time a building is occupied, the risks are far more difficult and expensive to address. That is why both guidance and legislation place significant responsibility on designers, principal contractors, and dutyholders to manage Legionella risks throughout the entire project lifecycle.
The Key Legislation: What the Law Actually Says
Several pieces of UK legislation and guidance apply to Legionella control within the construction sector. The primary pieces of legislation include:
- The Health and Safety at Work etc. Act 1974 (HSWA)
This Act sets out the general duty to prevent risks to health from workplace activities. Anyone responsible for designing, installing, or overseeing water systems must ensure that these systems do not create avoidable health risks, including the risks posed by Legionella.
- The Control of Substances Hazardous to Health Regulations 2002 (COSHH)
Legionella bacteria are classified as a hazardous substance under COSHH. This regulation requires employers and dutyholders to:
- Assess the risk of exposure to Legionella
- Implement appropriate controls to minimize or eliminate exposure
- Prevent or reduce exposure through ongoing monitoring
- Provide relevant training for staff and contractors
In construction, this means that Legionella risks must be assessed during the design, installation, commissioning, and ongoing maintenance of water systems.
- The Management of Health and Safety at Work Regulations 1999
These regulations reinforce the requirement to assess risks during the planning stages of any project. This is particularly critical for water systems, as improper planning can lead to stagnation, temperature loss, or unnecessary complexity in pipework—all of which contribute to Legionella growth.
- HSE Approved Code of Practice (ACoP) L8
ACoP L8 is one of the most widely referenced pieces of guidance for Legionella control. For construction projects, it requires:
- A Legionella risk assessment to be completed
- A written scheme of control to be established
- Competent personnel to be involved in the design and installation processes
- Ongoing monitoring until handover
ACoP L8 also clearly states that water system risks must be considered during the design phase,not just after installation.
- HSG274 Part 2 (Hot and Cold Water Systems)
This is the practical guidance that Legionella professionals use daily. It provides instructions on:
- Correct pipe routing
- Acceptable temperature ranges for water
- Commissioning requirements
- Avoidance of dead legs and redundant pipework
- Flushing requirements for low-use periods
- HSG274 is especially relevant for mechanical and plumbing contractors, designers, and commissioning engineers.
Design Stage: The Most Important Point for Legionella Control
Legionella control becomes much more complicated, and expensive, if issues are only discovered after installation. The law expects dutyholders to manage risks early, which is why the design stage is arguably the most crucial phase for preventing future problems.
Why a Legionella Risk Assessment at the Design Stage Is Crucial
A Legionella risk assessment conducted during the design stage can help to:
- Prevent unnecessary pipe runs and dead legs
Design reviews can identify redundant or oversized pipework before installation begins, reducing the risk of stagnation. - Ensure temperature control is achievable
Water systems must be able to maintain temperatures of at least 60°C in calorifiers and 50°C on return lines, with cold water systems kept below 20°C. A risk assessment ensures that these requirements can be met. - Specify appropriate materials
Certain materials are more prone to harbouring biofilm, which can increase the risk of Legionella growth. Choosing the right materials from the start helps reduce this risk. - Ensure adequate insulation
Thermal gain and heat transfer are common problems in new builds. Early design decisions can mitigate these issues and reduce the risk of Legionella. - Plan for sufficient access and maintenance points
Ensuring that systems are accessible for future monitoring, testing, and maintenance is a key aspect of effective Legionella control. - Avoid stagnation during construction
The risk assessment can outline specific flushing schedules, temporary measures, and commissioning plans to prevent water stagnation while the building is under construction.
In summary, a Legionella risk assessment completed during the design stage reduces risks, prevents costly rework, and ensures that the system is compliant from day one.
Who Holds Responsibility on Construction Projects?
Under UK law, several stakeholders share responsibility for Legionella management during a construction project:
- Designers
Designers must ensure that their designs do not introduce foreseeable Legionella risks. This includes considerations such as pipe sizing, routing, insulation, and the avoidance of dead legs. - Principal Contractors
Principal contractors are responsible for managing risks during construction, which includes ensuring that temporary water supplies are adequately controlled and that systems are kept flushed and protected. - Building Owners / Clients
Building owners and clients retain responsibility for ensuring that Legionella risks are considered from the very beginning of the project. - Commissioning Engineers
Commissioning engineers must ensure that water systems are properly tested, flushed, disinfected, and commissioned in accordance with HSG274 guidelines. - Water Hygiene Specialists
Water hygiene specialists should be involved early in the project to provide guidance, conduct risk assessments, and oversee the management of Legionella risks.
Failure to fulfill responsibilities at any of these stages can result in enforcement action, civil claims, or involvement from the Health and Safety Executive (HSE).
Common Construction Mistakes That Lead to Legionella Issues Later
Even the best-intentioned projects can face issues when Legionella control is not considered from the outset. Common mistakes include:
- Oversized water systems that lead to poor water turnover
- Abandoned or capped pipework, creating dead legs
- Stagnation during slow construction periods
- Lack of proper onsite flushing regimes
- Incomplete or poor commissioning documentation
- Temporary water supplies left uncontrolled
These issues often become apparent during pre-handover sampling or within the first few months of occupancy, leaving clients frustrated and requiring costly corrective work.
Putting a Legionella Management Plan in Place
A compliant construction project should include:
- A design-stage Legionella risk assessment
- A written scheme of control for construction and commissioning
- Documented flushing regimes
- Temperature monitoring for temporary systems
- Proper disinfection and commissioning before handover
- Clear handover documentation for the building owner
This approach not only protects the health of building users but also safeguards your project from delays, disputes, and enforcement action.
Legionella compliance in construction is not something to be considered after the build is completed. It is a legal requirement that starts at the design stage and continues throughout installation, commissioning, and handover.
A Legionella risk assessment conducted during the design stage is one of the most effective ways to prevent long-term issues, protect building users, and ensure that the project fully complies with the Health and Safety at Work Act, COSHH, ACoP L8, and HSG274.