What is the difference between a written scheme of control and a log book?
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Key points
- The written scheme is the plan; the log book is the record. Plan versus proof.
- The scheme comes from the risk assessment and is updated when it changes; the log book is added to continuously, every time a check is done.
- They must agree with each other: a scheme task with no matching log entries is a control that exists only on paper.
- Records are kept for at least five years; the scheme is kept current.
- Neither document certifies anything. One states intent, the other evidences execution.
A written scheme of control is the plan for managing legionella risk in your water system: what controls are in place, how often each task happens, and who is responsible. A log book is the record of that plan being carried out: the dated temperatures, flushes, inspections, and actions, entry by entry. The scheme says what should happen; the log book proves it did, and you need both, agreeing with each other.
They are often treated as one document, which is how schemes end up with blank record pages stapled to the back and nobody sure which half matters. Each is covered separately in written scheme of control and legionella log book; this page is about the relationship.
The two compared
| Written scheme of control | Log book | |
|---|---|---|
| What it is | The plan: control measures, frequencies, responsibilities, escalation actions | The record: dated evidence of each task actually carried out |
| Written when | After the risk assessment, before routine operation | Continuously, every time a task is done |
| Updated when | The system changes, the assessment is reviewed, or a control proves unworkable | Never rewritten; entries are added, errors corrected by a new entry |
| Typical contents | System description, task list with frequencies, named responsible persons, actions on failed checks | Temperature readings, flushing records, inspection reports, disinfection certificates, sample results, corrective actions |
| Kept for | Kept current; superseded versions retained with the records | At least five years |
| Proves | That the risk was assessed and a considered control regime exists | That the regime was actually carried out, day by day |
Why you need both
Each document answers a question the other cannot. An inspector, insurer, or court asking about your water system really asks two things: did you work out what needed to be done, and did you do it. The scheme answers the first; the log book answers the second. A scheme without a log book is a promise; a log book without a scheme is activity without rationale, flushing and measuring with nothing that says why these tasks, at these frequencies, were the right ones.
The risk assessment sits upstream of both. It identifies the risks; the scheme converts the findings into scheduled tasks; the log book records execution; and the findings in the log book, a persistent temperature failure, a fouled tank, feed back into the next assessment. That is the loop described in legionella management, and the scheme and log book are its middle two links.
The consistency test
The quickest health check on anyone's paperwork is to cross-read the two documents. Take a task from the scheme, weekly flushing of the named little-used outlets, monthly sentinel temperatures, the annual tank inspection, and look for the matching entries in the log book. If the scheme promises eight outlets on the flushing list and the log shows four, one of the documents is wrong, and it is usually the log. Auditors and inspectors do exactly this cross-check, because it is where paper compliance and actual compliance part company. Gaps should be recorded as gaps, with the reason and the corrective action, never silently back-filled.
The scheme says what should happen; the log book proves it did. Read together they are your defence. Read separately, each one can be made to say almost anything.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
Keeping them in step
Practically, the two documents work best created together, so every line of the scheme has a matching record sheet. The written scheme template and log book template are built as a pair for that reason, and the risk assessment builder generates the scheme's task list directly from the findings, so the plan and the record structure never drift apart. Keep the scheme current when anything changes, keep the log entries honest when anything goes wrong, retain both for at least five years, and remember the standing discipline: these documents record and structure your control regime. Neither one, however tidy, certifies a water system as safe.
Free legionella risk assessment template
A structured Word document following the five-step approach in ACOP L8. Covers risk identification, written scheme, monitoring, and records. If it isn't written down, you can't evidence it.
Follows ACoP L8 and HSG274 Part 2. Free. No spam.
Frequently asked questions
What is the difference between a written scheme of control and a log book?
The written scheme of control is the plan: it lists the control measures your risk assessment decided on, the frequency of each, who is responsible, and what to do when a check fails. The log book is the record: dated entries showing each check, flush, inspection, and action actually carried out. The scheme says what should happen; the log book proves it did. You need both, and they must agree with each other.
Is a legionella log book a legal requirement?
ACOP L8 requires records to be kept of the risk assessment, the written scheme, and the monitoring and control measures carried out, and it expects records kept for at least five years. A log book is the standard, practical way of meeting that requirement: one place where every temperature check, flush, inspection, and corrective action is written down. The legal requirement is for the records; the log book is how most duty holders satisfy it.
What should a written scheme of control contain?
A written scheme identifies the water system and its components, states the control measures chosen in the risk assessment, sets the frequency of each task such as weekly flushing or monthly temperature checks, names who is responsible for each, describes how the checks are carried out, and sets out the action to take when a check fails, for example an outlet that will not reach temperature. It is a living document, updated when the system or the assessment changes.
How long must legionella records be kept?
The general expectation under ACOP L8 is that monitoring and control records are kept for at least five years. That includes temperature records, flushing logs, inspection reports, disinfection certificates, and sample results. The risk assessment and written scheme themselves are kept current, but superseded versions are worth retaining with the records, because they show the history of how the system was managed, which is exactly what an inspector, insurer, or court will ask about after an incident.
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