Legionella Compliance (ACOP L8): Monitoring Frequencies Explained

Legionella Compliance (ACOP L8): Monitoring Frequencies Explained

Legionella is the compliance regime with the widest gap between how boring the routine is and how serious the failure mode gets. The routine is monthly thermometer readings and running taps; the failure mode is an outbreak inquiry, corporate manslaughter exposure, and a building in the news. Landlords, facilities managers, and employers all carry the duty — and most of the failures HSE finds aren't exotic: they're missed monthly checks and a risk assessment nobody reviewed.

Here's what the framework actually requires, the standard frequencies, and a free monitoring log.

The Framework: L8 and HSG274

Duties flow from the Health and Safety at Work Act and COSHH. The Approved Code of Practice L8 (Legionnaires' disease: the control of legionella bacteria in water systems) sets out what duty holders must do; HSG274 is the technical guidance that turns it into tasks and frequencies (Part 2 covers hot and cold water systems — the part that applies to almost every building; Part 1 covers cooling towers).

The structure is always the same four steps:

1. Risk assessment — by a competent person, identifying where legionella could grow (dead legs, storage tanks, showers, little-used outlets, temperature ranges of 20–45°C).
2. Written control scheme — who does what, at what frequency, and what happens when a reading is out of range.
3. Monitoring — the routine checks below, recorded.
4. Review — the risk assessment reviewed regularly and whenever the system or its use changes materially.

The Core Monitoring Routine (Hot & Cold Water Systems)

The two headline numbers: hot water should reach ≥50°C within one minute at the outlet (55°C in healthcare); cold should be ≤20°C within two minutes. The 20–45°C band in between is where legionella multiplies.

(Frequencies are HSG274 Part 2 starting points — your written risk assessment takes precedence, and cooling towers run a stricter Part 1 regime of their own.)

The weekly flushing line deserves emphasis because it's the one that fails first: the empty office, the spare shower, the mothballed floor. Stagnant water in the 20–45°C band is precisely the growth condition, and post-pandemic building underuse turned this from a footnote into the main event. If an outlet isn't used weekly, someone has to run it — and record that they did.

The Recording Problem

Legionella compliance is unusually record-heavy for how simple the tasks are: a 12-outlet building generates hundreds of dated readings a year, each needing a number, a pass/fail against the limits, and an action trail when out of range. The paper log book in the plant room works until it's missing the week the environmental health officer asks — and the reading nobody wrote down is legally a check that never happened. It's the compliance record-keeping problem at its highest frequency.

Three sheets: monthly temperature log with the limits built into the header, weekly flushing log, and the full HSG274 task schedule with your risk-assessment details.

When to Move Beyond the Spreadsheet

The template handles one building with one diligent person. The regime scales badly on paper: multiple buildings multiply outlets; staff turnover breaks the weekly habit; and out-of-range readings need an escalation trail, not just a cell turned red. Alongside the other clocks a building runs — fire extinguishers, PAT, LOLER lifts, emergency lighting — water hygiene is usually the highest-frequency regime in the whole compliance calendar, which makes it the one that benefits most from scheduled tasks with mobile completion: the technician logs the temperature at the outlet, out-of-range triggers an action, and the log book is a report you pull, not a binder you hope is complete.