What Is a Written Scheme of Control — And Does Your Business Need One?

If you've had a legionella risk assessment, the report probably recommended that you "implement a written scheme of control." And if you're like most building managers, your next thought was: "What on earth is a written scheme of control?"

It sounds bureaucratic. It sounds complicated. But it's actually one of the most practical documents in your water safety armoury — and yes, you almost certainly need one.

The Short Answer

A written scheme of control is a document that sets out exactly how you're going to manage legionella risk in your water system on an ongoing basis. It takes the findings and recommendations from your legionella risk assessment and turns them into a practical, day-to-day management plan.

Think of the risk assessment as the diagnosis. The written scheme is the treatment plan.

The Legal Basis

The requirement comes from the HSE's Approved Code of Practice L8 (Legionnaires' disease: The control of legionella bacteria in water systems). L8 states that where the assessment identifies a risk, the duty holder must prepare a written scheme for preventing or controlling the risk.

This isn't guidance — it's an Approved Code of Practice, which means that while it's not technically law, failure to follow it is likely to be used as evidence of non-compliance in any enforcement action. In practice, you should treat it as a mandatory requirement.

What Should It Contain?

A good written scheme of control covers several key areas:

Roles and responsibilities. Who is the duty holder? Who is the appointed responsible person for water safety? Who carries out the routine monitoring tasks? Who reviews the scheme? Every role should be named, with contact details and a clear description of their responsibilities.

Description of the water system. A schematic or written description of the water system, including cold water storage tanks, hot water generation (calorifiers, boilers), distribution pipework, outlets, and any ancillary systems (cooling towers, spa pools, decorative fountains). This should be kept up to date as the system changes.

Risk assessment summary. The key findings from the risk assessment, including the identified risks and their priority ratings. This provides the context for everything else in the scheme.

Control measures. The specific actions required to manage the identified risks. These typically include temperature control parameters (hot water stored at 60°C minimum, distributed at 50°C minimum, cold water below 20°C), flushing regimes for infrequently used outlets, cleaning and disinfection schedules, treatment programmes (chemical dosing, if used), and dead leg elimination.

Monitoring schedule. A detailed timetable of routine monitoring activities: what needs to be checked, how often, what parameters are being measured, and what the acceptable ranges are. Typical monitoring activities include monthly hot water temperature checks at sentinel outlets, monthly cold water temperature checks, quarterly checks at representative outlets throughout the system, and annual calorifier inspections and cleans.

Recording requirements. What records need to be kept, in what format, and for how long. Temperature logs, flushing records, maintenance records, inspection reports, water sampling results and corrective action records all need documenting.

Corrective actions. What happens when a monitoring result falls outside the acceptable range. If a cold water temperature comes back at 24°C, what's the procedure? Who gets notified? What investigation is triggered? What remedial action is taken?

Review schedule. When and how the scheme is reviewed. This should happen at least annually, and immediately after any significant changes to the water system, building use, or occupancy.

Who Prepares It?

The written scheme should be prepared by someone competent in legionella risk management. In practice, it's usually produced as part of, or immediately following, the legionella risk assessment. The assessor who understands your water system and has identified the risks is best placed to specify the control measures and monitoring regime.

The duty holder doesn't need to write it themselves — but they do need to understand it, implement it and ensure it's followed.

The Common Problems

The most frequent issue isn't the absence of a written scheme — it's having one that exists on paper but isn't implemented in practice. Temperature checks that should happen monthly but don't. Flushing regimes that are specified but nobody's doing them. Corrective actions that are documented but never followed up.

The second most common problem is a scheme that hasn't been updated. The building has been refurbished, new outlets have been added, old ones have been removed — but the scheme still describes the original installation.

A written scheme is only useful if it's current and actively followed.

Do You Definitely Need One?

If your legionella risk assessment identifies any risk that requires ongoing management — and for most commercial buildings, it will — then yes, you need a written scheme of control. That covers offices, hotels, care homes, schools, hospitals, leisure centres, residential landlords with communal water systems, and essentially any building with a water system that serves multiple outlets.

The only premises that might not need one are those where the risk assessment concludes that the risk is negligible and no ongoing controls are needed. For most buildings, that's not the case.

Need a written scheme of control for your premises? Book a Legionella Risk Assessment →

York Green Safety Partners provides legionella risk assessments with comprehensive written schemes of control for premises across the UK. Based in Cheshire, covering the whole country.