What is legionella monitoring?

Legionella monitoring is the set of routine checks that shows your water system's controls are still working: temperatures taken at chosen outlets, little-used outlets flushed, shower heads cleaned, tanks and calorifiers inspected, and every result written down. It runs on a calendar of different frequencies, from weekly flushing to an annual review, and it is the part of legionella management that never stops. The risk assessment is a snapshot; monitoring is the film.

This page is the hub for the monitoring cluster. It explains what a monitoring regime is, what it watches, and how the pieces fit together, and it points to the detailed guides on each part: the monitoring schedule, sentinel outlets, weekly checks, annual checks, and the monitoring log sheet.

What a monitoring regime actually is

Under ACOP L8, a duty holder must appoint a competent person, assess the risk, prepare a written scheme of control, and then implement, manage and monitor that scheme. Monitoring is the last link in that chain. It is how you know the scheme is real and not just a document in a drawer. The regime is built from four ingredients:

• Tasks. The specific checks: take this temperature, flush that outlet, inspect this tank. Each one exists because the risk assessment found something it controls.
• Frequencies. How often each task runs. HSG274 Part 2 gives the usual starting points, and the risk assessment adjusts them for your building.
• Targets. What a good result looks like: hot at 50°C or more within a minute (55°C in healthcare), cold below 20°C within two minutes, calorifier storage at 60°C or above. The temperature chart sets out the numbers.
• Records. The written log of every check and every action. Keep them at least five years.

The four things every regime watches

Whatever the building, a monitoring regime is watching the same four conditions, because they are the four things legionella needs:

• Temperature. Water between about 20°C and 45°C is the growth range. Monitoring confirms hot stays hot and cold stays cold. See temperature control.
• Movement. Stagnant water is where legionella establishes. Flushing records show little-used outlets are turned over before they stagnate. See flushing little-used outlets.
• Cleanliness and condition. Scale, sediment and biofilm shelter and feed the bacteria. Inspection and cleaning records show tanks, calorifiers, shower heads and thermostatic mixing valves are being kept in a condition that does not harbour growth.
• The record itself. The log book is evidence the other three are being watched. A regime with no records is indistinguishable from no regime at all.

The monitoring loop: measure, compare, act, review

A working regime is a loop, not a list. Each check follows the same cycle: measure something, compare it against the target, act if it is out of range, and record all three steps. When a sentinel outlet will not reach 50°C, the loop does not end at writing down the number. It continues into finding out why, whether that is a failing thermostatic mixing valve, a calorifier set too low, or a circulation problem, and recording what was done. How you monitor legionella walks through the task stack in detail.

Once a year the loop widens into a full review: are the controls still the right ones, has the building or its use changed, and does the risk assessment need revisiting. That is the subject of the annual checks.

Monitoring is not testing

The most common confusion in this area is between monitoring and sampling. For a typical hot and cold water system controlled by temperature, routine monitoring means thermometers, log sheets and physical inspections, not laboratory bottles. Sampling is a separate, targeted activity: the risk assessment may call for it, a system that cannot hold temperature may need it, and any positive result changes what the regime has to do next. Sampling and action levels explains when testing applies and what the results mean.

Where the regime lives: the log book

Everything the regime produces, temperatures, flushes, inspections, cleaning, actions, lands in one place: the log book. A simple bound book or folder works for a small premises; a digital log makes missed checks easier to spot. Our legionella log book tool lets you record each check as you do it, and the temperature monitoring template gives you a printable sheet for the monthly round. If you are starting from scratch, the risk assessment builder helps you work out which checks your system actually needs, and the temperature checker tells you whether a reading you have taken is in range.

The regime a monitoring programme serves is set by the written scheme of control, which in turn comes from the risk assessment. Monitoring is the daily and weekly reality of that chain of documents. It does not certify a system as safe, and no log book ever can. What it does is produce the continuous, dated evidence that the controls you chose were carried out, and that when they failed, someone noticed and acted.