ACOP L8 & HSG274 Part 2: what you actually have to do.
ACOP L8 is the law. HSG274 is the how. Together they tell duty holders — landlords, schools, care homes, facilities managers — exactly what temperatures to hit, how often to check them, and what records to keep. This page sets it out plainly.
The numbers you need to hit.
HSG274 Part 2 sets clear pass/fail thresholds for hot and cold water systems. These are not targets — they are the minimum legal standard. NHS premises have an additional, tighter requirement under HTM 04-01.
What is ACOP L8?
ACOP L8 — formally Legionnaires’ Disease: The Control of Legionella Bacteria in Water Systems — is an Approved Code of Practice (ACOP) issued by the Health and Safety Executive under the Health and Safety at Work etc. Act 1974.
An ACOP has a specific legal status: if you follow it, you will normally be doing enough to comply with the relevant law. If you do not follow it, a court can use that failure as evidence of non-compliance. It is not advisory — it is the standard against which duty holders are measured.
ACOP L8 applies to any water system where Legionella bacteria could grow and spread, including hot and cold water services in residential blocks, schools, hospitals, care homes, hotels, and commercial buildings.
What is HSG274 — and which part applies to you?
HSG274 is the supplementary guidance that explains how to implement ACOP L8 in practice. It is published in three parts, each covering a different type of water system.
Cooling towers, evaporative condensers, and adiabatic coolers. Relevant to commercial HVAC.
Calorifiers, hot water cylinders, cold water storage tanks, and the distribution pipework in buildings. This is the part most relevant to schools, housing associations, care homes, and local authorities.
Spa pools, vehicle wash systems, humidifiers, dental equipment water lines, and emergency safety showers.
How often do you need to check?
HSG274 Part 2 sets out a minimum monitoring schedule for hot and cold water systems. The frequency depends on the type of outlet and its role in the system.
Passing once a month is not a water safety programme.
The traditional approach to L8 compliance is a contractor visit once a month. A temperature is taken, a box is ticked, a log sheet is filed. If the reading passes, the building is recorded as compliant. Job done.
The problem is that a monthly check is a single data point. It proves the temperature was correct for one minute in thirty days — and nothing about the other 43,199 minutes in between. A system that routinely runs cold overnight, or drops out of range during school holidays, will still produce a passing monthly log if the contractor happens to visit on a good day.
Continuous monitoring changes this entirely. Instead of one reading per month, you have a timestamped record for every minute of every day. You can show — and prove — that the system was within range 99% of the time, not just that it happened to pass the one day someone came to look.
“If a Legionella case is traced to your building, the question is not whether you passed the monthly check. It is whether you can demonstrate the system was under control at the time of exposure.”
A single monthly log sheet cannot answer that question. A continuous audit trail can.
What it costs to get it wrong.
Prosecution under the Health and Safety at Work etc. Act 1974 carries unlimited fines in the Crown Court, and up to two years’ imprisonment for individuals found to have been grossly negligent. In cases where a Legionella exposure results in death, organisations can face charges under the Corporate Manslaughter and Corporate Homicide Act 2007.
The HSE publishes enforcement notices and prosecution outcomes publicly. Fines in the hundreds of thousands of pounds are not unusual for organisations that have failed to implement and maintain a documented water safety programme. Reputational damage — particularly for social landlords, schools, and care providers — compounds the financial penalty.
Critically, the defence “we had a contractor check it monthly” is only as strong as the evidence behind it. If an investigation reveals that the system was not actually under control between visits, the log sheet becomes evidence of a tick-box exercise, not a safety programme.
Compliance that pays for itself.
Continuous temperature monitoring does more than prove you are compliant. It shows you exactly what is happening to your water systems at all hours — including when no one is in the building.
A common and costly problem in schools, offices, and housing blocks is hot water systems running at full temperature during evenings, weekends, and school holidays. The boiler fires, the calorifier maintains 60 °C, the circulation pump runs — consuming energy and wearing out plant — for a building that is completely empty. Without monitoring, no one notices. With it, you can see the pattern, set appropriate setback schedules, and recover those running costs.
Equally, the data identifies when something in the system is not behaving as expected: a cold water tank warming above 20 °C on a hot summer day, a calorifier that is struggling to maintain temperature, a TMV that has drifted. These are not just compliance failures waiting to happen — they are maintenance issues that get cheaper the earlier they are caught.
See exactly when your hot water system is running in an empty building and schedule setback periods during holidays and evenings.
A TMV that has drifted 2 °C costs almost nothing to fix. The same fault discovered after an HSE investigation costs considerably more.
Not that you passed once. That you have been in control every day — which is the standard the law actually expects.
Temperature logs, alert history, corrective actions and TMV records in one place, retained for the required five years, available on demand.
Who is responsible?
Under ACOP L8, the duty holder is the person who is in control of the premises, or who has the ability to direct how water systems are managed. In practice:
Responsibility can be delegated to a competent person or a water hygiene contractor — but the legal liability remains with the duty holder. Delegation is not a defence.
What records do you need to keep?
ACOP L8 and HSG274 require duty holders to keep written records demonstrating that the water safety plan has been implemented. Records must be retained for a minimum of five years and made available to the HSE or a Local Authority Authorised Officer on request.
- Date, time, and location of each temperature check
- The temperature reading at each point
- The name of the person who carried out the check
- Whether the result was within the acceptable range
- Any corrective action taken and when
- Dates and outcomes of TMV servicing and inspections
- Any changes to the water system and their dates
The device built for HSG274 Part 2.
The Wavetrend LoRaWAN water temperature monitor clips onto pipes and reads hot, cold, and blended outflows simultaneously — the three-point configuration HSG274 Part 2 describes for sentinel outlet testing. Ten-year battery life. No plumber required.
Read the thinking behind it.
- Read →HSG274 vs ACOP L8 — what's the difference?One is the code you must follow. The other is how to follow it.
- Read →Does continuous monitoring meet HSG274?The guidance asks for temperatures, on a schedule, written down. Sensors do all three.
- Read →29 days you can't see: the gap in monthly Legionella checksA monthly check proves one minute. The risk has the rest of the month.
Want to know what proper L8 compliance looks like on your estate?
Short call. We’ll scope what a first deployment covers, which outlets to monitor, and what the evidence looks like on day one — not just on check day.