The number people ask for is the per-sample lab fee, and it is the least useful figure in the whole exercise. A single sample analysed by a UKAS-accredited laboratory is usually a modest, two-figure cost. Everything expensive sits around it: getting a competent person to site, collecting the samples properly, and deciding what to do when one comes back positive.
So the honest answer to “how much does it cost?” is that the lab analysis is the cheap part. Price the visit, the decision and the retest loop instead. That is where the money actually goes.
Stop pricing the sample, start pricing the visit
A quote that reads “£X per sample” hides the structure of the cost. Laboratory analysis is close to a commodity. What varies site to site is how many points you sample, who collects them, how far they travel, and how fast you need the result.
Two questions decide most of your spend. How many sample points does your risk assessment actually justify? And is that number set by the system in front of you, or by a contractor’s standard package? HSE is clear that monitoring and sampling frequency is driven by the system and the written risk assessment, not by a fixed timetable [1][2]. Sampling everything “to be safe” is the most common way to turn a sensible test into an expensive one.
There is a skill cost hidden here too. A sample taken from the wrong outlet, in the wrong sequence, or without the right pre- and post-flush detail tells you very little, and BS 7592 sets out what competent collection and point selection should look like [3]. A cheap visit that produces a misleading result is the most expensive test of all, because you pay again to repeat it.
The real cost drivers
Here is where the money goes, grouped by whether it is planned spend, friction, or failure. The ranges are illustrative — they show the shape of the cost, not anyone’s invoice.
| Driver | Type | What moves it | Illustrative weight |
|---|---|---|---|
| Lab analysis per sample | Planned | Culture vs PCR; Legionella species vs full serogroup breakdown; turnaround | Tens of pounds per point |
| Sample collection / call-out | Planned | Competent person’s time, travel, site access, number of points per visit | Often dwarfs the lab fee |
| Number of sample points | Planned | What the risk assessment justifies vs a standard package | Scales the whole bill |
| Express turnaround | Friction | Needing a result in a day or two rather than the standard window | A premium on each sample |
| Repeat mobilisations | Friction | Sending someone back for points missed first time | A second full visit cost |
| The retest loop | Friction | A positive triggers resampling, review and confirmation | Multiplies a single test |
| Chasing and reconstructing records | Friction | Results buried in inboxes and spreadsheets at audit time | Quiet, recurring labour |
| A confirmed case or outbreak | Failure | Investigation, enforcement, remediation, reputational harm | Orders of magnitude more |
The pattern is the point. Planned costs are predictable and you can design them down. Friction costs are leaks — repeat visits, chasing PDFs, retests triggered by a sample that was never going to answer a useful question. Failure costs are rare and enormous, and they are the reason the whole regime exists.
Typical cost bands
To put planning figures on that, here are illustrative bands from typical published UK rates — not a price list, and easily moved by how many points you sample, who collects them and how far they travel.
- Lab analysis, per sample. Usually tens of pounds — illustratively around £20 to £60 for a standard Legionella culture, with PCR or a fuller serogroup breakdown costing more per sample.
- The sampling visit (call-out plus the competent person’s time). Often the larger line, illustratively in the low-to-mid hundreds of pounds for a visit, scaling with travel, access and how many points are taken in one trip.
- A small routine sampling round — a handful of points collected and analysed — frequently comes to somewhere in the low-to-mid hundreds of pounds all-in, of which the lab fees are usually the smallest part.
Express turnaround, repeat mobilisations and the retest loop push these up. Because the visit dominates and packages bundle different things, compare current written quotes for the same points and turnaround rather than the headline per-sample price.
Where the spend pays back
Testing is verification, not control. A clean result never makes water safe; flushing, temperature management and a sound risk assessment do that. So sampling pays back only when it answers a question you genuinely need answered.
It pays back when your routine monitoring suggests control is drifting, when the risk assessment flags a specific concern such as a dead leg or a calorifier running cool, after remedial work to confirm it actually worked, and where your scheme or guidance calls for it — cooling towers, spa pools, and higher-risk settings such as healthcare premises being the clearest cases [2][4].
It does not pay back when sampling becomes a substitute for control: testing more often to compensate for a flushing programme nobody runs. That spends money to discover a problem you could have prevented for less. The pragmatic call is to fix the cheap, high-frequency control first, then sample to confirm — not the other way round.
How to justify the spend internally
The comparison that lands with a budget holder is not test-cost versus zero. It is test-cost versus failure-cost. A confirmed case can trigger reporting under RIDDOR and an HSE investigation, with an immediate demand for the records that show a controlled scheme [5]. Against that, a year of sensible sampling is a rounding error.
The cheapest improvement is rarely negotiating the lab fee down. It is cutting friction: sampling the right points once instead of the wrong points twice, batching collection into fewer visits, and producing audit-ready evidence without a scramble. Moving temperature logs, flushing records and sample results off paper and spreadsheets into a digital logbook is where a lot of estates quietly recover the cost — the evidence is there when an auditor asks, and you stop paying people to reconstruct it after the fact.
Treat all of this as general guidance to weigh through your own competent, site-specific risk assessment. The figures above are illustrative shapes, not a price list, and only your assessment can say how many points your particular system warrants or how often.
The concrete move this week is dull and revealing: pull your last twelve months of testing invoices and split each one into three lines — lab analysis, the visit, and any retests. The lab line is almost always the smallest. Then check every sampled point against your current risk assessment, and you will usually find a few you are paying to test for no documented reason.
FAQ
Why is the per-sample price so different between providers?
Because the headline price often bundles different things. One quote may be lab analysis only; another includes the competent person’s time, travel and a call-out charge. Analysis scope also varies — a basic count versus a full serogroup breakdown — as does turnaround. Compare the whole job, not the per-sample line.
Does PCR testing cost more than culture?
Typically yes per sample, and it answers a different question: PCR is fast and detects genetic material, while culture grows and counts viable bacteria and is the long-standing reference method [4]. Faster is not automatically better value. Choose the method that fits the decision you need to make, then price it.
How often do we have to sample, and does that drive the cost?
Frequency is the single biggest cost lever, and it is set by your system and written risk assessment, not by a standard package [1][2]. There is no universal interval. A stable, well-controlled low-risk system may need very little routine sampling; a cooling tower or a flagged concern needs more. Get the frequency right and the bill follows.
Sources
[1] HSE, “Testing and monitoring your water system for legionella”. https://www.hse.gov.uk/legionnaires/testing-monitoring-water-system.htm [2] HSE, “Legionnaires’ disease: Technical guidance (HSG274)”. https://www.hse.gov.uk/pubns/books/hsg274.htm [3] BSI, “BS 7592:2022 - Sampling for Legionella bacteria in water systems. Code of practice”. https://knowledge.bsigroup.com/products/bs-7592-sampling-for-i-legionella-i-bacteria-in-water-systems-code-of-practice-1 [4] CDC, “Laboratory Testing for Legionella”. https://www.cdc.gov/legionella/php/laboratories/index.html [5] HSE, “RIDDOR - Reporting of Injuries, Diseases and Dangerous Occurrences Regulations”. https://www.hse.gov.uk/riddor/