How Often Does a Legionella Risk Assessment Need to Be Done?

If you have recently had your first legionella risk assessment, you may be wondering how long it is valid for and when you will need to have it done again. The answer is not quite as straightforward as a fixed annual date — it depends on the type of property, the complexity of your water systems, and whether anything changes between assessments.

This guide explains the review timescales required under UK law, the circumstances that trigger an earlier reassessment, and what ongoing management you are expected to carry out between formal reviews.

The Legal Position on Assessment Frequency

The Health and Safety Executive's Approved Code of Practice, ACoP L8, does not set a single fixed frequency for legionella risk assessments. Instead, it requires that the assessment is reviewed 'regularly' and whenever there is reason to suspect that it may no longer be valid.

In practical terms, the industry standard — and what the HSE considers appropriate for most premises — is a full review every two years for routine domestic and commercial properties. However, this is a minimum expectation, not a ceiling. Higher-risk premises, or those where conditions change frequently, will require more regular reassessment.

Assessment Frequency by Property Type

Standard Domestic Rental Properties

For a straightforward single-let property with a modern combi boiler, mains-fed cold water, and simple pipework, a review every two years is typically sufficient — provided the water system has not changed, the property has remained occupied throughout, and no issues have been identified.

HMOs and Properties with Cold Water Storage Tanks

HMOs with complex water systems — multiple bathrooms, shared facilities, cold water storage tanks, or older pipework — should be reassessed annually in most cases. The higher risk profile of these properties, combined with the higher tenant turnover and variable water usage, means that a two-year gap between formal assessments is often too long to maintain appropriate control.

Commercial Premises

Commercial properties follow similar guidance to residential, but the review frequency should be set in the Written Scheme of Control following the initial assessment. Higher-risk commercial premises — such as care homes, hotels, leisure centres, and healthcare facilities — will typically require annual review and more frequent interim monitoring.

Triggers for an Earlier Reassessment

Even if your last assessment was recent, you must carry out a new assessment if any of the following apply:

• There have been significant changes to the water system, pipework, or associated equipment

• The use of the building has changed — for example, a residential property converting to an HMO

• A new tenancy begins following an extended void period

• You become aware of new information about legionella risks that may affect your property

• Monitoring results indicate that your current control measures are not working effectively

• There has been a suspected or confirmed case of Legionnaires' disease associated with the property

What Needs to Happen Between Assessments?

A legionella risk assessment is not a substitute for ongoing management. Between formal reviews, you are expected to follow the Written Scheme of Control produced as part of the assessment. This typically includes monthly water temperature monitoring at sentinel outlets, quarterly showerhead descaling and disinfection, periodic flushing of infrequently used outlets, and annual review of the Written Scheme itself.

Failing to carry out this ongoing monitoring is a compliance breach, even if your risk assessment is current. The assessment sets the framework — the ongoing management is what keeps your water system safe.

How We Help You Stay on Schedule

When East Midlands Legionella carries out your risk assessment, we add your property to our compliance calendar and contact you before your next review is due. We also provide you with a monitoring schedule appropriate to your property so that you know exactly what checks need to be carried out and when.

Don't leave your business at risk.