A Legionella Risk Assessment is not a one-off requirement. To remain compliant with ACoP L8 and HSG274 guidance, assessments must be reviewed regularly to ensure that risks remain controlled and that any changes to the system are properly managed.

In most cases, a Legionella Risk Assessment should be reviewed at least every two years, although the exact frequency depends on the complexity of the water system and the level of risk identified.

What Do ACoP L8 and HSG274 Say?

ACoP L8 does not set a strict fixed timeframe for reassessment. Instead, it requires duty holders to ensure that their risk assessment remains suitable and sufficient at all times.

HSG274 guidance supports this by recommending that assessments are reviewed periodically and whenever there is reason to believe that the original assessment may no longer be valid.

When Should a Legionella Risk Assessment Be Reviewed?

In addition to regular periodic reviews, a reassessment should be carried out if there are significant changes to the system or its use.

Common triggers include:

• Changes to the water system (e.g. new tanks, pipework, or outlets)
• Changes in building use or occupancy
• Evidence that control measures are no longer effective
• Water quality issues or microbiological results
• After any remedial works or system alterations

These changes can introduce new risks or alter existing ones, making it essential to reassess the system.

Does Every Building Need the Same Review Frequency?

No — the frequency of review depends on the level of risk.

For example:

• Low-risk systems (simple domestic-type systems) may require less frequent review
• Higher-risk systems (complex commercial systems, healthcare environments) may require more regular assessment

A competent assessor will recommend an appropriate review period based on the specific system and its risk profile.

What Happens If You Don’t Review Your Risk Assessment?

Failing to review your Legionella Risk Assessment can lead to:

• Outdated or inaccurate risk information
• Ineffective control measures
• Increased risk of Legionella growth
• Non-compliance with ACoP L8

In the event of an inspection or incident, an outdated assessment can also make it difficult to demonstrate that you have taken reasonable steps to manage risk.

How to Stay Compliant

To maintain compliance, you should:

• Review your Legionella Risk Assessment regularly
• Monitor your water system in line with your control scheme
• Keep accurate records of all checks and actions
• Update your assessment when changes occur

Many organisations choose to combine regular reviews with ongoing monitoring and compliance support to ensure risks are consistently managed.

Do You Need a New Assessment or Just a Review?

In some cases, a simple review of the existing assessment may be sufficient.

However, a new Legionella Risk Assessment may be required if:

• The existing report is significantly outdated
• There have been major system changes
• The original assessment is no longer considered reliable

A professional review will determine whether an update or a full reassessment is needed.

Conclusion

A Legionella Risk Assessment should typically be reviewed every two years, but more frequent reviews may be required depending on the system and any changes that occur.

Maintaining an up-to-date assessment is a key part of managing Legionella risk and ensuring compliance with ACoP L8.