You can run a faultless control regime and still come unstuck. If the temperatures, flushes and cleans never make it onto paper or into a system in a form someone else can follow, the work might as well not have happened - because to an auditor, an HSE inspector, or whoever inherits the building after you leave, the logbook is the evidence that any of it took place.
That is the whole job of a Legionella logbook: to turn the things you do into things you can prove. Get that idea straight and the rest is detail.
What a logbook actually is
A Legionella logbook is not a diary, and it is not a drawer full of receipts. It is the structured record that shows your written scheme of control is being carried out, that exceptions are being caught, and that someone competent is keeping an eye on the whole thing. UK guidance under the Approved Code of Practice (L8) expects duty holders to keep records of the precautions taken, the monitoring carried out, and the management arrangements behind them [1].
In practice that means one place - a paper binder, a spreadsheet, or a dedicated app - that holds, or clearly points to:
- the current risk assessment and the written scheme of control;
- who the responsible person is, who deputises, and what they are competent to do;
- routine monitoring such as sentinel tap temperatures, calorifier flow and return, and cold tank checks;
- flushing of little-used outlets, plus cleaning or descaling of shower heads and hoses;
- tank inspections, disinfections, and any sampling results;
- and the part people skip: what happened when a reading came back wrong.
How it works on a real site
Picture a mid-sized office. On the first Monday of the month a maintenance operative walks the sentinel outlets with a probe thermometer. The hot taps should reach temperature quickly; the cold should stay cold. Each reading goes in against the specific asset, with a date, a name, and a simple in-range or out-of-range flag.
Most months everything is fine and the entries are dull. Then one cold tap reads 23 degrees C because a hot riser is warming the pipe behind the wall. A useful logbook does not just record “23, out of range” and move on. It records that the reading was escalated to the responsible person, what was decided - say, increased flushing and a check on the pipe insulation - and the date the follow-up reading came back in range and the action was closed.
That chain - who, when, which asset, what result, in or out of range, and what was done about it - is the spine of a good record. A logbook full of unbroken green ticks and no exceptions is not reassuring. More often it means nobody is really reading the thermometer.
Myth versus reality
A handful of instincts about record keeping quietly let people down.
| What people assume | What’s actually true |
|---|---|
| Every box ticked means the building is compliant | A logbook records activity. Compliance is whether the controls work and whether exceptions were acted on - a tidy book over a weak scheme proves the wrong thing |
| Going digital automatically improves the records | Software enforces timestamps and structure, but a badly set-up app just produces neat noise faster. The thinking still has to happen |
| The contractor’s visit sheets are our logbook | Their reports are inputs. The duty holder still needs the oversight record and a live list of open actions [3] |
| Once a task is signed off, the entry is finished | The entries that matter most are the out-of-range ones: what was found, what was done, and when it was closed |
| You either keep everything forever or bin it after a year | Retention carries defined expectations; keep records long enough to cover audit, handover and any incident review [1] |
Record the decision, not just the task
New compliance managers tend to record the task and forget the reasoning. “Flushed outlet - done” tells a future reader nothing. “Outlet flushed weekly because the room is used intermittently; missed flushes escalate to the responsible person; three misses trigger a review of whether the outlet should be capped” tells them why the control exists and what good looks like.
Write down the why, not only the what. It is the difference between a record that survives an awkward question and one that invites more of them. Monitoring frequencies and acceptable results come from your risk assessment, not from a template [2] - so note where each figure originated, and the logbook starts to defend itself. The same habit makes the audit trail readable to anyone who picks it up cold, which is the real test.
Read your own records like an auditor
You do not need to buy anything to begin. Pull your current records together and read them as if you had walked in to inspect the building.
- Can you find the risk assessment and written scheme in under a minute?
- For last month’s monitoring, can you name who took each reading and when?
- Find one out-of-range result. Can you trace it to an action and a close-out?
- If you left tomorrow, could your replacement run the scheme from the logbook alone?
If any answer is “no”, you have found your first fix - and that gap is exactly what an inspection or a suspected case would expose. For the monitoring routine the logbook is meant to capture, covers flushing and temperature checks; for the full set of documents a compliant file should hold, see on essential records.
A note on limits
A logbook proves what you did; it does not decide what you should do. The tasks, temperatures and frequencies inside it come from a competent, site-specific risk assessment, not from this page - and a beautifully kept book sitting over a control scheme nobody has reviewed in years is its own kind of risk. Treat the records as evidence of control, never as a stand-in for it.
FAQ
What records belong in a Legionella logbook?
At a minimum: the risk assessment and written scheme, the named responsible person and their deputies, routine temperature monitoring, flushing of low-use outlets, cleaning and disinfection, any sampling results, and the actions taken when something fell out of range. L8 frames these as records of the precautions, the monitoring and the management arrangements [1].
How long should we keep Legionella records?
Longer than you might expect, and for a defined period rather than indefinitely. Guidance attaches retention expectations to monitoring and management records so they cover an audit and any later investigation; confirm the exact durations that apply to your records against current HSE guidance [1].
Is a digital logbook acceptable, or does HSE want paper?
The format is not the point - the evidence is. Paper, spreadsheet or app are all acceptable if the record reliably shows who did what, when, to which asset, with what result, and what followed any exception [3]. Digital usually wins on legibility, search and a tamper-evident audit trail; a simple paper book can still work on a small, low-risk site.
Sources
[1] 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 [2] HSE, “Legionnaires’ disease: Technical guidance (HSG274)”. https://www.hse.gov.uk/pubns/books/hsg274.htm [3] HSE, “Legionnaires’ disease - what you must do”. https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm