There is no licence to print, no single certificate that turns someone into a qualified Legionella risk assessor. UK law asks for a “competent person” to carry out the assessment, then leaves the duty holder to decide what competent actually means. That can feel like being asked to mark an exam in a subject you do not teach.

It is checkable, though. Competence here is a blend of water-system knowledge, relevant training and a method you can watch working — and you can interrogate all three before any money changes hands.

What you are actually buying

A Legionella risk assessment is not a tick-box survey. It is the decision document your whole control programme hangs off: it describes the water system, finds where the bacteria could grow or be breathed in, judges who is exposed, and sets the precautions that follow. Buy a weak one and everything downstream — your written scheme, your monitoring, your spending — inherits its blind spots.

So you are buying judgement, not paperwork. HSE guidance is plain that the duty holder must appoint someone competent to carry out the assessment, and competence means the right ability, experience, instruction, training and resources for that particular system [1][2]. A domestic plumber who has sat a half-day course is not automatically competent to assess a multi-wing care home with calorifiers, thermostatic mixing valves and long dead legs. The work has to match the building.

How to vet an assessor before you sign

Treat the appointment like any other procurement. Define what good looks like, ask for evidence, and pay attention to what the assessor quietly avoids answering.

What a competent assessor brings

  • Real water-systems knowledge. They can talk fluently about cold-water storage, calorifiers, dead legs, TMVs and where stagnation hides — not just recite temperatures back at you.
  • Training matched to your building’s complexity. A single low-risk office is a different job from a hospital wing or a block of flats.
  • A method tied to recognised standards. BS 8580-1 is the British Standard code of practice for Legionella risk assessment, and a credible assessor works to it alongside the technical detail in HSG274 [3][4].
  • A site visit, not a desk exercise. Assessing an occupied building means eyes on the plant, the outlets and the asset register — not a form filled in from a phone call and a floor plan.
  • Reasoning you can see. If the same firm wants to sell you the remedial works it recommends, that is not automatically wrong, but you should be able to follow the logic behind every recommended pound of spend.

Questions worth asking before you appoint

  • Who, specifically, will attend site, and what experience do they have with buildings like mine?
  • Do you work to BS 8580-1, and will the report map its findings back to it?
  • Are you a registered member of the Legionella Control Association, and can I see your audit status? Registration means the provider has been independently audited against a published code of conduct [5].
  • What does the report give me beyond a list of faults — does it risk-rank actions, name owners and set review triggers?
  • What would a review or re-visit cost, and when would you say one is due?

Red flags

  • A fixed price quoted with no site visit and no questions about your system.
  • A template report with your address pasted into someone else’s findings: generic wording, no photographs, no schematic.
  • Pressure to buy chlorination or tank cleaning immediately, before the assessment is even written.
  • An assessor who cannot explain, in plain terms, why a particular outlet is a risk.
  • No insurance, no references, no named individual — just a logo on a quote.

If a provider clears the criteria, answers the questions without flannel and trips none of the red flags, you have done the diligence the law expects of you.

In-house, sole trader or registered firm?

Not every building needs an external assessor. A simple, lower-risk premises with a trained, genuinely competent responsible person can carry out and record its own assessment — the law allows it, provided that person really has the competence and the time to do it properly [1]. The trade-off is honesty about your own limits. In-house keeps cost down and site knowledge in the building, but it leans entirely on one person’s training staying current and their judgement staying independent.

A sole trader can be excellent and cheaper, though continuity is worth a thought: who covers your reviews if they retire or fall ill? A registered firm costs more and can feel impersonal, but brings audited processes, professional indemnity and depth of cover. There is no universally right answer, only the right answer for your building’s complexity and how much risk you are willing to carry yourself. a companion guide weighs that choice in detail.

The duty you cannot sign away

One point deserves to be blunt. Appointing a competent assessor does not move the legal duty off your desk. The duty holder stays accountable for the system, for the adequacy of the assessment, and above all for acting on what it finds [2]. A respected logo on the cover is no defence if the document sits unread in a drawer. Judge any assessor against your own site, your own use patterns and your own circumstances rather than a glossy brochure — and where a recommendation carries a specific number, such as a temperature, a review interval or a sampling frequency, confirm it against current HSE guidance and the assessor’s reasoning instead of taking it on trust. This is general guidance, not a substitute for that site-specific judgement.

Common questions

Is there an official Legionella risk assessor qualification or licence in the UK?

No single statutory licence exists. The law requires a competent person, and competence is shown through relevant training, experience and a sound method rather than one named certificate. Registration with the Legionella Control Association is a useful signal, because it means the provider has been audited against a code of conduct [5].

Can I carry out my own Legionella risk assessment?

You can, for a straightforward, lower-risk building, if you are genuinely competent and have the time to do it well and keep it current [1]. As soon as the system gets complex — healthcare premises, multiple buildings, vulnerable occupants — most duty holders are better served by an experienced external assessor.

What is the difference between an LCA-registered provider and any other contractor?

An LCA-registered provider has submitted to independent auditing against the association’s code of conduct; an unregistered contractor may be perfectly competent but offers you no third-party check of that claim [5]. Registration is evidence to weigh, not a guarantee — you still vet the individual who turns up on site.

Sources

[1] HSE, “Legionnaires’ disease - what you must do”. https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm [2] HSE, “Legionnaires’ disease. The control of legionella bacteria in water systems - Approved Code of Practice and guidance (L8)”. https://www.hse.gov.uk/pubns/books/l8.htm [3] BSI, “BS 8580-1:2019 - Risk assessments for Legionella control. Code of practice”. https://knowledge.bsigroup.com/products/water-quality-risk-assessments-for-legionella-control-code-of-practice-1 [4] HSE, “Legionnaires’ disease: Technical guidance (HSG274)”. https://www.hse.gov.uk/pubns/books/hsg274.htm [5] Legionella Control Association, “Code of Conduct for Service Providers”. https://www.legionellacontrol.org.uk/