A legionella risk assessment can be carried out by anyone the Health and Safety Executive (HSE) considers a “competent person,” meaning someone with sufficient training, experience, and knowledge to properly identify and evaluate legionella risks in a water system. There is no single mandatory qualification or license required. In some cases, a building manager or landlord can do it themselves. In others, particularly for complex water systems, hiring a specialist consultant is the practical choice.
What “Competent Person” Actually Means
The HSE defines a competent person as someone with “sufficient training and experience or knowledge and other qualities” to assist you properly. That definition is deliberately broad. It doesn’t name a specific certification or degree. Instead, it places the burden on you, as the duty holder, to ensure whoever carries out the assessment genuinely understands legionella risks, water system design, and the control measures needed to manage them.
The British Standard BS 8580-1:2019, which covers risk assessments for legionella control, places particular emphasis on assessor competence. Its most significant updates specifically address the skills a risk assessor should have and the quality of the report they produce. The standard calls for competent individuals who can produce “brief, clear, user-friendly reports lacking superfluous information.” In practice, this means the assessor needs to understand water system layouts, temperature profiles, how biofilm develops, where stagnation occurs, and how to translate all of that into actionable recommendations.
When You Can Do It Yourself
For simple water systems, particularly domestic rental properties, you may not need to hire anyone at all. The National Residential Landlords Association confirms that landlords are not required to hire a professional for a legionella risk assessment. If you feel competent to evaluate the system yourself, that’s legally acceptable. A typical domestic property with a straightforward hot and cold water setup, no complex storage tanks, and no long runs of unused pipework is relatively simple to assess.
A self-assessment in this context involves checking water temperatures at taps, looking for dead legs (sections of pipe that no longer serve an outlet), confirming the hot water cylinder stores water above 60°C, and ensuring cold water stays below 20°C. If the property has no cooling towers, spa pools, or unusual plumbing arrangements, the risk profile is low and manageable without specialist help. But if you’re unsure about any part of the process, the guidance is clear: bring in a professional.
When You Need a Specialist
Larger or more complex buildings almost always require an external consultant. Hospitals, schools, leisure centres, care homes, hotels, and commercial premises with cooling towers or extensive hot and cold water networks present risks that go well beyond a basic checklist. The assessor needs to physically inspect the entire water system, measure temperatures at multiple outlets, check disinfectant levels, assess the condition of storage tanks, identify areas of low flow or stagnation, and evaluate whether existing control measures are working.
A thorough on-site assessment involves running hot water taps until they reach maximum temperature, recording both the temperature and how long it took to get there, then repeating the process for cold water. The assessor measures disinfectant concentrations and pH levels at sampling points throughout the building. They also review system schematics, maintenance records, and any previous monitoring data. This level of detail requires someone who understands the ecology of legionella bacteria and how building water systems create conditions for bacterial growth.
Consultants registered with the Legionella Control Association (LCA) are widely regarded as the industry benchmark in the UK. LCA members must meet specific standards for training, service delivery, and quality management. While LCA registration isn’t a legal requirement, it provides a level of assurance that the assessor has been independently vetted.
Independence Matters
One principle that runs through legionella management guidance is the separation between assessment and maintenance. The person or company that carries out your risk assessment should ideally be independent of whoever is responsible for maintaining the water system day to day. This avoids conflicts of interest. If the same contractor both maintains your system and assesses whether it’s safe, there’s an obvious incentive to overlook problems.
International guidance reinforces this. Best practice holds that anyone who develops a water management plan or provides treatment services should not also be responsible for monitoring whether that plan is effective. Testing should be independent of those responsible for maintenance. When hiring a consultant, choosing someone who has no financial interest in selling you ongoing treatment services gives you a more objective assessment.
What Happens Without a Proper Assessment
The consequences of getting this wrong are serious. Legionella risk assessment is a legal requirement under UK health and safety law, and enforcement carries real penalties. In one notable case, Amey Community Limited was fined £600,000 after a prisoner died at HMP Lincoln in 2017. The company had actually conducted a risk assessment in 2016 but failed to act on its findings. There was no written scheme in place to prevent and control legionella risks in the prison’s water system. The company pleaded guilty to breaching the Health and Safety at Work Act.
The key lesson from that prosecution isn’t just that you need an assessment. You need a competent assessment, and you need to follow through on its recommendations. A risk assessment that sits in a filing cabinet without being implemented offers no legal protection.
How Often Assessments Need Updating
A legionella risk assessment isn’t a one-time exercise. It should be reviewed regularly and updated whenever something changes. Triggers for a new assessment include modifications to the water system, changes in building use, refurbishment work, periods when parts of the building sit unused, or any indication that control measures aren’t achieving the right results. If routine monitoring shows that recommended temperatures or disinfectant levels aren’t being consistently maintained, that’s a signal the assessment needs revisiting.
For open systems like cooling towers and spa pools, the HSE recommends routine testing at least quarterly. Hot and cold water systems in enclosed buildings may need less frequent testing, but monitoring should increase whenever there’s doubt about how well the control regime is performing. Many organizations review their full risk assessment every two years as standard practice, though this isn’t a fixed legal interval.
Choosing the Right Assessor
When selecting someone to carry out your assessment, look for demonstrable training in legionella risk management, practical experience with your type of building or water system, and familiarity with current standards including BS 8580-1:2019 and the HSE’s Approved Code of Practice (known as L8). Ask whether they hold relevant qualifications from recognized training providers, how many assessments they’ve completed on similar premises, and whether they carry professional indemnity insurance.
LCA membership is a strong indicator but not the only one. Some highly experienced consultants operate outside the LCA framework. What matters most is that the assessor can demonstrate genuine competence, produces a clear and actionable report, and has no conflict of interest with the ongoing maintenance of your system. The report itself should identify specific risks, recommend proportionate control measures, and be written so that whoever manages the building can understand and act on it without needing a water engineering degree.