Legionella Written Scheme of Control: What to Include and How to Write One

A written scheme of control is the operational backbone of legionella compliance. If the risk assessment identifies the hazards, the written scheme documents what you are doing about them — who does what, when, and how.

ACoP L8 requires duty holders to prepare and implement a written scheme proportionate to the risk in their water system. For a landlord with a simple domestic system, this may be a brief document. For complex buildings with cooling towers or large distribution networks, a detailed multi-section scheme is expected. Here is what it should contain and how to write one that will satisfy an inspector.

What a written scheme of control is

The written scheme of control ties together all of your legionella control measures into one document. Think of it as an operating manual for your building's water hygiene management.

It answers four questions:

1. What control measures are in place?
2. Who is responsible for each task?
3. What is the monitoring schedule?
4. What happens when something goes wrong?

HSG274 Part 2, Appendix 2.2 provides guidance on the content of a written scheme for hot and cold water systems.

The 6 sections every written scheme needs

1. System description

A concise description of the building's water system:

• Water supply source (mains, private supply)
• Hot water generation (combi boiler, stored cylinder, calorifier, point-of-use heaters)
• Cold water storage (tank, direct mains feed)
• Distribution: a list or schematic of all pipe runs and outlets
• Any high-risk features: dead legs, long pipe runs, infrequently used outlets, TMVs

This section should reference the risk assessment — the two documents work together.

2. Named responsible persons

Role	Name	Responsibilities
Duty holder	[Property owner/manager]	Overall legal responsibility for compliance
Responsible person	[Named individual]	Day-to-day management of the written scheme
Deputy	[Named individual]	Covers during absence

For a landlord with a small portfolio, the duty holder and responsible person are often the same person. For larger organisations, these roles are typically separated.

3. Control measures

Document each control measure, mapped to the hazards identified in the risk assessment:

Hazard	Control measure	Standard
Hot water temperature	Store at 60°C+, deliver at 50°C+ at outlets	ACoP L8, HSG274 Table 2.1
Cold water temperature	Maintain below 20°C at outlets	ACoP L8, HSG274 Table 2.1
Stagnant water	Weekly flushing of outlets unused for 7+ days	HSG274 Part 2
Biofilm/scale	Quarterly showerhead descaling and disinfection	HSG274 Part 2
Dead legs	Remove dead legs where possible; flush remaining dead legs weekly	ACoP L8
TMV function	Annual servicing and functional testing	Manufacturer guidance (HTM 04-01 applies to healthcare settings specifically)

4. Monitoring and recording schedule

A clear timetable of checks, who performs them, and where the records are kept:

Task	Frequency	Performed by	Records location
Hot water outlet temperature	Monthly	[Name/role]	Temperature log
Cold water outlet temperature	Monthly	[Name/role]	Temperature log
Hot water storage temperature	Monthly	[Name/role]	Temperature log
Flushing of infrequent outlets	Weekly	[Name/role]	Flushing log
Showerhead descaling	Quarterly	[Name/role]	Cleaning log
TMV servicing	Annually	Specialist contractor	Service record
Risk assessment review	Every 2 years (or after changes)	[Name/role]	Risk assessment file

5. Corrective action procedures

What to do when something goes wrong:

Temperature failure: If a monthly temperature check returns a reading outside thresholds (hot below 50°C at outlet, cold above 20°C):

• Investigate the cause within 24 hours (thermostat setting, insulation, pipe routing)
• Re-check after correction
• Record the failure, investigation, and corrective action
• If the failure cannot be resolved: consult a water hygiene specialist

Positive legionella sample (if testing is performed):

• Isolate the affected system or outlet immediately
• Notify the responsible person and, depending on concentration, the local authority
• Arrange disinfection
• Investigate root cause
• Review and update the risk assessment
• Record all actions

Missed monitoring tasks:

• Perform the missed task as soon as identified
• Record the gap and the reason
• Review whether any additional risk exists (e.g., an outlet was not flushed for three weeks — flush for longer and monitor temperature)

6. Review and update log

The written scheme is a living document. Record every update:

Date	Change	Reason	Updated by
[Date]	Initial written scheme created	New assessment	[Name]

Review the written scheme whenever the risk assessment is reviewed, when the water system changes, or when monitoring reveals a pattern of non-compliance.

How it connects to the risk assessment

The risk assessment and the written scheme are two halves of the same compliance framework:

Document	Purpose	When updated
Risk assessment	Identifies hazards and assesses risk	Every 2 years or after changes
Written scheme	Documents control measures and monitoring	Whenever the risk assessment changes, or procedures change

An inspector will expect to see both documents. The written scheme must reflect the current risk assessment — if the assessment identifies dead legs, the written scheme must include a flushing schedule for those dead legs.

Common mistakes

• Copying a generic template without editing it. The written scheme must be specific to your building. A template is a starting point, not a finished document.
• Not naming a responsible person. A scheme that says "the landlord will..." without naming who that is lacks accountability.
• No corrective action procedures. What happens when a temperature check fails? If the scheme does not address this, it is incomplete.
• Not updating after changes. Added a new shower room? Removed a dead leg? The written scheme must be updated to match.

Generate a written scheme for your building

A Written Scheme of Control Generator is planned for launch in the coming weeks. In the meantime, LegioLog's free tools can help you get started:

• Risk Assessment Template Generator — creates a building-type-specific risk assessment that the written scheme can reference
• Temperature Compliance Checker — check readings against L8 thresholds
• Flushing Schedule Calculator — generate a flushing schedule for section 4 of your scheme

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

This guide covers written scheme of control requirements under ACoP L8 and HSG274 Part 2 for England, Wales, and Scotland. This is general compliance guidance, not legal or professional advice — for site-specific schemes, consult a competent person.

Sources

• HSE — ACoP L8: Legionnaires' disease
• HSE — HSG274: Legionnaires' disease technical guidance