UK Legionella Testing Requirements: What the Law Says in 2026

"Legionella testing" means different things depending on who you ask. A landlord reading about testing requirements will find conflicting advice — some sources say it is legally required, others say it is not. Both can be correct, because they are talking about different things.

Here is what UK law actually requires, broken down by the three types of legionella "testing."

The three types of legionella testing

Type	What it is	Legally required?
Risk assessment	A documented assessment of your water system's legionella risk	Yes — for all duty holders
Temperature monitoring	Regular checks that water temperatures are outside the 20-45°C growth zone	Yes — ongoing monitoring is required under ACoP L8
Microbiological testing	Laboratory analysis of water samples for legionella bacteria	Not usually — only in specific circumstances

Most of the confusion comes from conflating these three activities.

Risk assessment requirements

Every duty holder must have a documented legionella risk assessment. This is the legal baseline — without it, you cannot demonstrate compliance.

The assessment identifies hazards in your water system and sets out the control measures needed. It must be reviewed regularly (at least every two years) and updated after any changes to the water system or building use.

For landlords of simple residential properties, self-assessment is permitted. For complex systems, a specialist assessor is needed.

See our guide to risk assessments for landlords for the full process.

Temperature monitoring requirements

ACoP L8 and HSG274 Part 2 require ongoing temperature monitoring as a primary control measure. This means:

Monthly checks:

• Hot water at sentinel outlets: must reach 50°C or above within one minute of running
• Hot water storage (cylinder/calorifier): must be 60°C or above
• Cold water at sentinel outlets: must be below 20°C

Sentinel outlets are the nearest and furthest outlets from the hot water source — these represent the temperature extremes in your system.

What "monitoring" means in practice:

• Use a calibrated thermometer (digital probe thermometers are inexpensive and widely available)
• Run the outlet for one minute, then take the reading
• Record the reading with date, outlet location, temperature, and who performed the check
• Flag any readings outside thresholds for investigation

This is not optional. Temperature records are the primary evidence of ongoing compliance that inspectors look for after the risk assessment itself.

Use the Temperature Compliance Checker to verify your readings against L8 thresholds.

Microbiological testing — when it IS required

Routine microbiological testing (sending water samples to a lab for legionella culture) is not required for most domestic hot and cold water systems. HSE guidance does not mandate it for standard residential, commercial, or educational properties.

However, microbiological testing IS required or recommended in these circumstances:

Scenario	Testing required?	Notes
Cooling towers and evaporative condensers	Yes — quarterly minimum	HSG274 Part 1 requires routine monitoring
Healthcare settings (hospitals, clinics)	Yes — per HTM 04-01	More stringent than standard ACoP L8
After a legionella incident or positive sample	Yes	Verify that remediation has been effective
After prolonged building closure	Recommended	Verify system is safe before re-occupancy
Complex systems with persistent temperature failures	Recommended	If temperature control cannot be maintained, sampling confirms whether bacteria are present
Standard domestic hot and cold water	No	Risk assessment + temperature monitoring is sufficient

If you do commission microbiological testing, samples must be analysed by a UKAS-accredited laboratory to have any evidential value. You can search for accredited testing labs on the UKAS website.

Other ongoing requirements

Beyond the risk assessment and temperature monitoring, ACoP L8 requires:

• Flushing — weekly for outlets unused for seven or more days. See our flushing guide.
• Showerhead cleaning — quarterly descaling and disinfection
• TMV servicing — annual where thermostatic mixing valves are installed
• Written scheme of control — documenting all of the above. See our written scheme guide.
• Record keeping — all monitoring, flushing, cleaning, and servicing must be recorded and available for inspection

What inspectors focus on

In a compliance check, inspectors typically ask for:

1. The risk assessment (documented, signed, reviewed within two years)
2. Temperature monitoring logs (regular, consistent, readings within thresholds)
3. Flushing records (if applicable — evidence of regular flushing of unused outlets)
4. The written scheme of control (ties everything together)

The absence of records is treated as non-compliance. Even if you have been performing all the checks, without written records you cannot demonstrate compliance.

Summary: what you must do

For most UK duty holders with standard hot and cold water systems:

• Must do: Risk assessment, temperature monitoring (monthly), flushing (weekly for unused outlets), showerhead cleaning (quarterly), record keeping, written scheme of control
• Do not need to do: Routine microbiological testing, "legionella certificates", annual professional inspections (unless system is complex)

For the full regulatory framework, see our ACoP L8 and HSG274 guide.

This guide covers legionella testing requirements under UK health and safety law as of 2026. Legislation and guidance may be updated — check the HSE website for the latest version of ACoP L8 and HSG274. This is general compliance guidance, not legal advice.

Sources

• HSE — ACoP L8: Legionnaires' disease
• HSE — HSG274: Legionnaires' disease technical guidance
• HSE — Legionella and Legionnaires' disease
• HSE — Legionella and landlords' responsibilities