ACOP L8 and HSG274, UK wide
Water Safety Plans and Written Schemes of Control
A legionella risk assessment tells you where the risk is. The written scheme of control is what stops that risk becoming a case of Legionnaires' disease eighteen months later. AL23 Safety writes water safety plans and written schemes of control, builds the monitoring regime around them and keeps both current, for duty holders UK wide.
What is a written scheme of control?
The operating manual for your water system
A written scheme of control is required by Approved Code of Practice L8. It describes the water system, states the safe operating conditions, sets out the precautions to be taken, names who carries out each check and at what frequency and defines what happens when a reading falls outside the control parameters. Without one, monitoring is just numbers in a book with nothing to compare them against.
A water safety plan is the wider governance document. It wraps the risk assessment, the written scheme, the responsible person structure, the monitoring records, the assurance regime and the incident response into one framework, usually overseen by a water safety group. In NHS premises that structure is expected by HTM 04-01. Outside healthcare it is good practice rather than a legal requirement. It is also the single best way we know of stopping a water system falling between the facilities team, the water treatment contractor and the people who actually use the outlets.
Who needs one
Anyone whose risk assessment found a reasonably foreseeable risk
- Any duty holder whose water system presents a reasonably foreseeable legionella risk, which in practice covers almost every non-domestic building with stored or heated water.
- Operators of wet cooling towers and evaporative condensers, who carry a separate notification duty on top of everything else.
- Care homes, hospitals, dental practices and primary care premises, where the population is more susceptible and the temperature regime is tighter.
- Schools, universities and boarding accommodation, where holiday shutdowns create long stagnation periods across a large distribution system.
- Landlords, managing agents and facilities managers with a repairing obligation, including those responsible for communal water services in residential blocks.
- Leisure operators running spa pools, swimming pools, splash features and vehicle wash systems, which fall under HSG274 Part 3 rather than Part 2.
- Any building running well below its design occupancy after a change in working patterns, where flow through the pipework has quietly collapsed.
The regulations that apply
Your legal framework, in plain terms
There is no Legionella Act. The duty comes from three places. Sections 2 and 3 of the Health and Safety at Work etc. Act 1974 set the general duties. The Control of Substances Hazardous to Health Regulations 2002 treat legionella as a biological agent. Regulation 3 of the Management of Health and Safety at Work Regulations 1999 requires the risk assessment. Operators of wet cooling towers and evaporative condensers are caught separately by the Notification of Cooling Towers and Evaporative Condensers Regulations 1992. The technical detail sits in ACOP L8 and in the three parts of HSG274.
ACOP L8, fourth edition, 2013
Legionnaires' disease: the control of legionella bacteria in water systems. Failure to follow an Approved Code of Practice is evidence of breach in criminal proceedings unless you can show you achieved compliance in an equally effective way.
HSG274 Part 1, reissued March 2024
Evaporative cooling systems. The 2024 review was the substantive one, updating the DPD No.1 test methodology and pH correction for halogen biocide efficacy.
HSG274 Part 2, reissued March 2024
Hot and cold water systems. This is where the monitoring regime that most buildings need comes from.
HSG274 Part 3, reissued March 2024
Other risk systems, including spa pools, humidifiers, vehicle wash systems, fountains, misting units and dental unit waterlines.
Notification of Cooling Towers and Evaporative Condensers Regulations 1992
Written notification to the local authority of every wet cooling tower and evaporative condenser on the premises. Written notification is required again when a device ceases to be used.
The responsible person, plus the deputy everyone forgets
L8 requires the duty holder to appoint a competent responsible person, a named individual with sufficient authority, competence and knowledge of the system to make the scheme work. It also expects a named deputy. In practice the deputy is where schemes fail. The responsible person leaves, the deputy was never briefed and monthly temperature monitoring stops for a year without anyone noticing. We put the appointment in writing, define what each person is authorised to decide and build the handover into the plan itself.
What the service covers
From the written scheme to the escalation route
- The written scheme of control, covering system description, schematics, control parameters, monitoring tasks, frequencies, responsibilities and the remedial action for each out of specification result.
- Verified schematic drawings. A scheme written against a system that no longer exists is worse than no scheme at all.
- Responsible person and deputy appointments in writing, with defined authority and a competence record behind each name.
- Water safety plan and water safety group terms of reference, membership, meeting frequency and reporting line, where the size or sensitivity of the estate justifies that governance.
- The hot and cold water monitoring regime built from HSG274 Part 2 and adjusted to your building rather than lifted from a template.
- Identification of little used outlets and a flushing regime that is genuinely achievable, with true dead legs listed for removal rather than flushed forever.
- Cooling tower and evaporative condenser management under HSG274 Part 1, covering local authority notification, weekly dip slide checks, the biocide dosing regime and legionella sampling at least quarterly.
- Other risk systems under HSG274 Part 3, including spa pools, humidifiers, misting and fogging units, vehicle wash, fountains and dental unit waterlines.
- Closed system management for heating and chilled water circuits, covering inhibitor levels, corrosion and bacteriological sampling, pressurisation, side stream filtration and the interface with the open systems those circuits serve.
- The scald and legionella conflict resolved properly, with thermostatic mixing valves specified, located close to the outlet and placed on a servicing regime, rather than the hot water being turned down.
- Record keeping, including a logbook structure your contractor and your auditor can both follow, with a stated retention rule.
- A defined escalation route for out of specification results, sampling positives and any suspected case, naming who contacts the local authority and when.
The frequencies and what status they actually have
This is where providers routinely overstate the law. The intervals below are recommendations from HSG274 Part 2. They are not statutory intervals. Your risk assessment can justify departing from them in either direction, provided the reasoning is written down.
Monthly
Temperature checks at sentinel outlets. Hot water should reach 50 degrees Celsius within one minute at the outlet. In healthcare premises the figure is 55 degrees. Cold water should be at or below 20 degrees within two minutes.
Monthly
Calorifier flow and return temperatures.
Quarterly
Calorifier hot water storage temperature, at or above 60 degrees Celsius.
Annually
Calorifier internal inspection or drain down.
Weekly
Flushing of little used outlets, run for long enough to replace the water sitting in the branch.
Quarterly
Showerhead and flexible hose descale and disinfection.
Annually
Cold water storage tank inspection.
Rolling annual
Representative temperature checks across all outlets, not only the sentinels.
Cooling towers, Part 1
Weekly dip slide or microbiological checks, with routine legionella sampling at least quarterly and more often where control is uncertain.
The same honesty applies to the review interval for the risk assessment. L8 requires review regularly and whenever there is reason to believe the assessment is no longer valid. It does not state a number of years. Two years is established industry convention and it is what most insurers expect. It is not a statutory requirement. Our legionella risk assessments page covers the assessment itself in detail.
Our process
Verify the system, set the regime, then audit
- 01
Read the system, not the file
We walk the plant rooms, tank rooms and risers, verify the schematic against reality and mark up everything that has been altered since the drawings were produced.
- 02
Set the control regime
We define control parameters, sentinel outlets, sampling points and monitoring tasks, then match each frequency to the risk rather than to a standard schedule.
- 03
Write the scheme and the plan
The written scheme of control, the responsible person and deputy appointments and, where the estate needs it, the water safety plan and water safety group terms of reference.
- 04
Hand over and train
We brief the responsible person, the deputy and the contractor together in the same room. Nobody can then claim the other party owned the task.
- 05
Audit and review
We audit the logbook against the scheme, take our own readings to test whether the recorded ones are real and rewrite the scheme when the system or the occupancy changes.
What you get
A scheme your caretaker can actually run
- A written scheme of control under ACOP L8, specific to your system and referenced to the relevant part of HSG274.
- Marked-up schematic drawings identifying storage, calorifiers, sentinel outlets, dead legs, sampling points and isolation.
- Written responsible person and deputy appointments with defined authority and a competence record.
- A monitoring schedule and logbook structure, task by task, with the frequency and the acceptance criteria printed alongside the task itself.
- Water safety plan and water safety group terms of reference where the estate justifies them.
- A prioritised remedial action plan separating what must be physically fixed from what must be monitored.
What we need from you
Your risk assessment, your schematics, your plant access
- Your current legionella risk assessment and the monitoring records for the last two years.
- Schematics, asset lists and plant room access, including tank rooms, roof spaces and any locked risers.
- Details of your water treatment or monitoring contractor and their current scope of works.
- Occupancy information, including any areas that are seasonal, dormant or running below design occupancy.
- The name of the person you intend to appoint as responsible person, plus their deputy.
Why AL23 Safety
We check the outlets your contractor forgot
Accountable
We will tell you when your contractor is monitoring the wrong outlets. We will also tell you when a logbook full of ticks does not match the temperatures we take on the day.
Expert and chartered
Qualified, chartered professionals working to ACOP L8 and to the March 2024 reissue of HSG274 Parts 1 to 3.
Practical, not just compliant
A scheme your caretaker can run beats a scheme only a specialist can interpret. We write for the person holding the thermometer.
UK wide
We write and maintain water safety documentation across the UK, from a single building to a national estate. It sits naturally alongside our health and safety in facilities management support.
One question worth asking today
Can your responsible person name their deputy?
If the answer is no, the scheme is not being managed, whatever the logbook shows. Send us your risk assessment and a plant list and we will tell you what is missing before an inspector does.
Common questions
Answers, up front
Cannot see your question? Get in touch and we will answer it directly.
Contact usThe requirement comes from Approved Code of Practice L8, which supports the Health and Safety at Work etc. Act 1974 and COSHH 2002. An ACOP carries special legal status. If you do not follow it you must be able to show you achieved the same standard by another route, otherwise a court may treat the failure as evidence of breach. In practice, if your risk assessment identifies a foreseeable risk you need a written scheme.
The written scheme is the technical control document for the system. The water safety plan is the governance wrapper around it, covering roles, the water safety group, escalation, incident response and assurance. A small building often needs only the scheme. Hospitals, care homes and large mixed estates need both. Our care home health and safety page shows how this works in a care setting.
No. They are recommendations in HSE technical guidance, not statutory intervals. They are nonetheless the benchmark an inspector, an insurer or a court will start from. Departing from them needs a documented reason recorded in the risk assessment, not a quiet decision by whoever holds the contract.
You do not choose between them. You keep the hot water system hot, storing at or above 60 degrees Celsius and distributing so the outlets reach their target temperature, then control the delivered temperature with thermostatic mixing valves fitted close to the outlet. The valves then need their own servicing, thermal performance checks and records. Turning the calorifier down to prevent scalding is the wrong answer and is a recurring enforcement finding.
Yes. The Notification of Cooling Towers and Evaporative Condensers Regulations 1992 require written notification to the local authority of every wet cooling tower and evaporative condenser on the premises. You must notify again when a device is taken out of use. That duty is entirely separate from your monitoring obligations under HSG274 Part 1.
Cost is driven by the number and complexity of the systems, whether usable schematics exist, how many outlets there are and whether cooling towers or Part 3 systems are involved. A scheme for a single building with a current risk assessment and good drawings is quick. Reconstructing schematics for an estate altered over thirty years is not. Send us a site list and your current risk assessment and we will price it properly.
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