Most duty holders need a risk assessor first, a water treatment or water hygiene company to run the day-to-day controls, and a standalone consultant only for complex sites or independent oversight. The job titles overlap and the marketing blurs them, but the decision underneath is simple: are you buying someone to assess and advise, or someone to carry out the work, and do you want those to be the same firm?
Get that prior decision right and the rest falls into place. Get it wrong and you either pay a consultant to do something a hygiene company does cheaper, or you let the firm that profits from remedial work also decide how much of it you need.
The three things you might actually be buying
Strip away the company names and there are only three distinct services on the table.
The first is an assessment: a survey that finds the dead legs, the cool calorifier and the rarely-used shower, and tells you what to control and in what order. The second is delivery: running the regime week after week, from temperature checks, flushing and TMV servicing to tank cleaning and, where genuinely needed, disinfection or chemical dosing. The third is advisory oversight: interpreting findings, designing the scheme of control, and giving a view independent of whoever holds the delivery contract.
Whoever you phone, you are buying one or more of those three.
What each provider type does
A risk assessor carries out the survey and writes the Legionella risk assessment, ideally to the methodology in BS 8580-1 [1]. It is a point-in-time job: they tell you what is wrong and what to fix, but do not usually stay on site to run the controls. If you have no current assessment, this is almost always your starting point, because you cannot buy a control regime sensibly until you know what needs controlling.
A water treatment or water hygiene company is the delivery arm. They turn the assessment into action: temperature monitoring, flushing little-used outlets, descaling shower heads, servicing TMVs, cleaning and disinfecting tanks and calorifiers, treating cooling towers, and dosing chemicals where the system calls for it. Many also carry out risk assessments in-house, which is where the lines blur. This is the provider most buildings have an ongoing relationship with.
A Legionella consultant sits above the hands-on work: interpreting the assessment, designing or challenging the written scheme of control, auditing your contractor, and giving a second opinion when something is contested. An independent consultant Legionella role earns its fee on complex, high-risk or disputed sites, not on a single low-risk office.
One firm often offers two or three of these under one roof. That is convenient and frequently fine, but it creates the incentive question below.
Side by side: who does what
The clearest way to place these is to compare the provider models on the axes a cautious buyer actually cares about, not on their brochure descriptions.
| Provider model | Core thing you get | Do they sell the remedial works? | Best when you need | Competence signal to check |
|---|---|---|---|---|
| Independent risk assessor | The BS 8580-1 survey and risk assessment, plus prioritised advice [1] | Usually no | A current, suitable assessment and an independent view of what to fix first | LCA registration for risk assessment, plus the named assessor’s training and experience [2] |
| Water hygiene / treatment company | Ongoing delivery: monitoring, flushing, servicing, cleaning, disinfection, dosing | Yes, this is their business | Someone to run the control regime week to week | LCA registration for the specific service categories they deliver [2] |
| Independent consultant | Interpretation, scheme design, audit, competent-person advice | Usually no | A complex or high-risk site, a dispute, or oversight independent of your contractor | Relevant qualifications and demonstrable independence from the delivery contract |
| Combined provider (assess + deliver) | Assessment and ongoing works under one contract | Yes | A single point of contact, where you accept and manage the incentive | Category-scoped LCA registration plus transparency on how advice is separated from sales |
Treat the table as a filter, not a verdict. No row is the “good” or “bad” option. Each fits a different situation, and the right answer for your building depends on its risk and your in-house capacity.
The incentive question to think about before you sign
Here is the consideration that worries the reader who has been pitched a chemical treatment they did not expect, and it applies to any trade: when the firm that recommends remedial work is also the firm that profits from carrying it out, there is a built-in incentive worth keeping in view. That is not an accusation against any provider. Plenty of reputable water hygiene companies that both assess and deliver manage this transparently and will show you the line in the risk assessment that justifies each measure. The point is a general buyer’s one: keep the question visible rather than assume it away.
So ask, do not suspect. When a recommendation lands, ask which finding in the risk assessment drives it, and whether the person who recommended it also invoices for it. A conflict of interest around chemical sales is managed, not eliminated, by separating the advice from the supply, or by getting the advice from someone who does not sell the cure.
LCA registration helps here as a neutral marker, not a ranking. Legionella Control Association registration signals that a provider has committed to a defined code of conduct and service standards. It is voluntary and service-category specific, so a firm registered for monitoring is not automatically registered for risk assessment [2]. Use it to confirm a provider is competent for the category you are buying. It does not make a consultant “better” than a hygiene company, or the reverse.
On the upsell fear specifically: in most low-risk hot and cold water systems the primary controls are temperature and movement, keeping hot water hot, cold water cold, stagnation out, and flushing infrequently used outlets. Chemical dosing is specified for particular cases, such as cooling towers or systems where reliable temperature control is not achievable, not as a default for a simple building [3]. If a quote for an ordinary office or rental leads with continuous chemical dosing, that is your cue to ask which assessment recommended it and why temperature control alone will not do.
Which one to phone first
Work it in order of what you already hold.
If you have no current risk assessment, start with a risk assessor, whether an independent one or the assessment arm of a hygiene firm. Everything else is guesswork until the survey exists, and a stale assessment should be reviewed when your system or its use has changed [4]. The questions worth putting to any assessor before you instruct them are set out in How to choose a Legionella risk assessment company (questions to ask), and what “competent” actually means for the person walking your site is covered in Who is qualified to perform a Legionella risk assessment?.
If you have a sound assessment and need the controls run, a water hygiene company is your provider. The duty stays with you even when they deliver the work, so the relationship has to be managed, not just bought; Working with contractors: ensuring Legionella compliance is the practical version of that. Whether you hand over every task or keep some in-house, such as routine temperature checks, is a separate call worth weighing in Outsourcing Legionella testing vs doing it in-house.
If you run a complex, high-risk or healthcare site, are in a dispute, or simply want oversight independent of the firm doing the work, that is when a consultant pays for themselves. For a single small low-risk building, it usually does not.
One fact does not move whichever provider you use: you, the duty holder, appoint the competent person and remain accountable for the outcome [5][6]. You are hiring competence to inform a duty that stays with you, not handing the duty away.
A caveat worth stating plainly
This is general guidance to help you choose a provider, not legal, medical or design advice, and it does not decide anything for your building. Which provider you need, and what controls are justified, come from a competent, site-specific risk assessment of your own systems, applied by someone who has seen them. The standards named here are codes of practice and technical guidance that inform that judgement rather than replace it. If you are being recommended a measure you do not understand, the right response is to ask for the assessment finding behind it, not to take this article as the answer.
What to do today
Find your most recent Legionella risk assessment and check two things: its date, and whether it still describes your building as it stands now. If it is missing or out of date, your first call is a risk assessor, not a treatment company, because you cannot judge any chemical or works quote without it. If the assessment is current, line every recommendation in a contractor’s proposal up against it, and ask the provider to point to the finding that drives each one. The recommendations that cannot be traced back to a finding are the ones to question first.
FAQ
Do I need both a Legionella consultant and a water treatment company?
Usually not. Most buildings need a risk assessor to produce the assessment and a water hygiene company to run the controls. A separate consultant is worth the spend on complex, high-risk or healthcare sites, where there is a dispute, or where you want oversight that is independent of the firm holding the delivery contract. For a simple, low-risk building, paying for a consultant on top is generally overkill.
Is it a conflict of interest if the same company does my risk assessment and the remedial work?
There is an incentive to be aware of, not an automatic problem. A firm that both assesses and delivers has a commercial interest in the works it recommends, which is true of many trades. Reputable providers manage that openly and can show you the assessment finding behind each recommendation. To keep it in check, ask which finding drives each measure, or take the assessment from someone who does not also sell the cure.
Should I worry about being sold chemical dosing I do not need?
Be questioning rather than worried. In most low-risk hot and cold water systems the primary controls are temperature and flushing, not continuous chemical treatment; dosing is specified for particular cases such as cooling towers or where temperature control is not achievable [3]. If a quote for an ordinary building leads with chemical dosing, ask which risk assessment recommends it and why temperature control alone is not enough.
Sources
[1] 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 [2] Legionella Control Association, “Code of Conduct for Service Providers”. https://www.legionellacontrol.org.uk/ [3] HSE, “Legionnaires’ disease: Technical guidance (HSG274)”. https://www.hse.gov.uk/pubns/books/hsg274.htm [4] 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 [5] HSE, “Legionnaires’ disease - what you must do”. https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm [6] HSE, “Hot and cold water systems”. https://www.hse.gov.uk/legionnaires/hot-and-cold.htm