Your training

Employers must protect their workers. That's the core duty.

And anyone else who might be affected. Visitors, residents, patients, the public.

Every other legionella regulation sits underneath this one. It's the foundation.

If your building has a water system that could expose people to legionella, this law applies.

If there's a foreseeable risk, you have a legal duty to manage it. L8 gives advice on HSWA sections 2, 3, 4 and 6

Legionella is a biological agent. Under COSHH, it counts as a hazardous substance — the same category as chemicals.

What it asks is straightforward: assess the risk, prevent exposure where you can, and control it where you can't prevent it entirely.

The bacteria grow naturally in water. You're not expected to make them vanish — you're expected to stop them reaching levels that could make someone ill. Control of Substances Hazardous to Health Regulations 2002, Regulations 6 & 7

ACOP L8 — Approved Code of Practice. This is the bridge between law and action. It has a special legal status: you don't have to follow it exactly, but if you don't, you must show your approach works just as well.

Think of it this way: L8 is the path that's already been checked. You can take a different route, but you need to prove it gets you to the same place safely.

In an investigation, following L8 is your strongest evidence of compliance. Choosing a different way isn't wrong — but you carry the burden of showing it works. L8 ACOP: Legionnaires' disease — The control of legionella bacteria in water systems (4th ed., HSE)

HSG274 and BS 8580. If L8 says what to do, these tell you how. Temperatures to hit, how often to test, which methods to use.

HSG274 comes in three parts: hot and cold water systems, cooling towers, and other risk systems like spa pools. Most buildings only need Part 2 — hot and cold water.

BS 8580 adds another layer — it helps you assess risk based on who is in your building. A care home with elderly residents needs tighter control than a warehouse with three staff. HSG274: Legionnaires' disease — Technical guidance (HSE); BS 8580-1:2019 (BSI)

Find the risk. Before anything else, look at your water system and ask: where could legionella grow? This is the risk assessment — and it must happen before controls, testing, or monitoring.

You're looking for places where water sits still, warms to between 20–45°C, or collects sediment. Dead legs, rarely used outlets, storage tanks without lids. L8 ACOP, paragraphs 29–35

Write it down. If you assessed it, record it. If you controlled it, record it. The written record is your proof that you took the risk seriously and acted on it.

Records must stay up to date and be available for inspection. This isn't paperwork for its own sake — it's the thread connecting what you found to what you did about it. L8 ACOP, paragraph 46

Do the work. Put the controls in place that your risk assessment identified. Temperature management, flushing, cleaning, disinfection — whatever your system needs.

Controls aren't one-off. They're ongoing. A monthly temperature check that stops being monthly isn't a control any more — it's a gap. L8 ACOP, paragraphs 36–45; HSG274 Part 2

Prove it. Monitoring confirms your controls are working. Temperature logs, test results, inspection records — these show that what you planned is actually happening.

If your records show a target of 60°C but your monitoring shows the water is regularly at 48°C, the control isn't working. The proof is in the numbers, not the intention. L8 ACOP, paragraphs 47–52; HSG274 Part 2, Section 2.3

Get help. You don't have to do this alone. The law expects you to use competent assistance — people who understand water systems and the controls that work.

That might be someone in-house or an external consultant. The key word is competent — they need to know your type of system, not just hold a qualification. We come back to this in Module 3. L8 ACOP, paragraph 25; Management of Health and Safety at Work Regulations 1999, Regulation 7

The dutyholder is the person in control. If you own the building, it's you. If you're the employer using the building, it's you. If you're a landlord letting it out, it's you.

It doesn't matter whether you know about legionella or not. The duty exists the moment you have control of a building where people could be exposed to water systems.

In a block of flats, it's the landlord or management company. In a school, it's the governing body. The question is always: who controls the premises? L8 ACOP, paragraphs 17–20

You can hand over the work. Flushing, testing, temperature checks, maintenance — all of these can be given to someone else.

What you're handing over is the task, not the duty. You're saying "please do this for me." You're not saying "this is no longer my problem."

The person you hand work to must be competent. If you hand flushing to someone who doesn't know why they're doing it, that's your gap, not theirs. L8 ACOP, paragraphs 22–24

Legal responsibility doesn't move. You can delegate every single task. The responsibility for making sure it all works stays with you.

If your contractor misses a month of testing, the regulator won't ask your contractor why. They'll ask you.

This isn't about blame. It's about ownership. The system in your building is yours to manage. Other people help — but the thread always leads back to you. L8 ACOP, paragraphs 17–18; HSWA 1974, Section 3

Start with a name. Not a job title, not a department — an actual person. "The facilities team handles water" is a gap. "Sarah Chen manages legionella controls for this building" is governance.

The named person should know they've been named, understand what it means, and have the time to do it properly. A name on paper without a conversation behind it is just paperwork. L8 ACOP, paragraph 22

Define what's covered. Which building? Which systems? Hot and cold? Cooling? Showers, taps, tanks? If the scope isn't written down, it's assumed — and assumptions create gaps.

If you have two buildings and the scope only covers one, the other building doesn't have a legionella control programme — it has a hope. L8 ACOP, paragraphs 22–24

Give them authority to act. If the person responsible spots a problem but has to wait three weeks for a budget sign-off, the authority isn't real.

Authority means: they can call a contractor, shut down an outlet, spend money within a defined limit — without asking permission first. The risk won't wait for your next board meeting. L8 ACOP, paragraph 22; HSG274 Part 2, Section 1.3

Build a way up. A legionella detection, a system failure, a budget they can't cover — there must be a clear route to someone with more authority.

Escalation isn't failure. It's the system working. The person on the ground reports upward, the dutyholder decides, and the record shows the chain. L8 ACOP, paragraphs 22–25

The responsible person is the day-to-day pair of hands. They're the one who makes sure flushing happens, temperatures get checked, and records get kept.

They're appointed by the dutyholder — not self-appointed, not assumed. The dutyholder decides who this person is and tells them.

This might be the building manager, the facilities lead, or a site caretaker. In a smaller building, it might be you — the dutyholder and responsible person in one. L8 ACOP, paragraphs 22–24

Competence does not mean a certificate on the wall. It means knowing THIS system in THIS building — where the tanks are, how the pipework runs, which outlets are rarely used.

The HSE defines it as the right combination of training, experience, and knowledge for the task at hand. A qualification helps — but without site-specific knowledge, it's not enough on its own.

A consultant with twenty years' experience who has never seen your building is not yet competent for your building. Someone who has walked your system every week for a year might be. L8 ACOP, paragraph 25; Management of Health and Safety at Work Regulations 1999, Regulation 7

One person can wear many hats. In a small building, the dutyholder might also be the responsible person, the risk assessor, and the one doing the weekly checks.

The risk is spreading too thin. If one person is doing everything — managing the building, handling complaints, ordering supplies, AND running the legionella programme — something gets missed.

That's legal. But it needs to be honest. If you're the one person, ask yourself: do I actually have time to do this properly? If the answer is no, appoint someone who does. L8 ACOP, paragraphs 22–25; HSG274 Part 2, Section 1.2

Write it down. A name, not a role. "The caretaker" is a gap. "James Osei, site caretaker, appointed 14 March 2025" is a record.

The appointment should be in writing. The person should know they've been appointed, understand what it means, and have accepted the role. L8 ACOP, paragraph 22

Say which system they're responsible for. Which building? Which water systems — hot, cold, both? Cooling towers? Showers in the sports block?

If you manage three buildings and the appointment letter only mentions one, the other two don't have a responsible person. They have an assumption. L8 ACOP, paragraphs 22–24; HSG274 Part 2, Section 1.3

Give them real authority. Can they call a plumber without asking? Can they shut off an outlet that's reading 30°C? Can they spend £200 on an emergency repair without a purchase order?

If the answer to any of those is "they'd need to check with someone first," the authority isn't real. Legionella doesn't wait for a sign-off chain. L8 ACOP, paragraph 24

Show them the way up. A positive legionella result, a system failure they can't fix, a cost they can't cover — there must be a clear route to someone with more authority.

Escalation isn't failure — it's the system working. The responsible person reports up, the dutyholder decides, and the record shows the chain. If there's no route up, the person you chose is on their own. That's not an appointment — it's abandonment. L8 ACOP, paragraphs 22–25; HSG274 Part 2, Section 1.2–1.3

A risk assessment is a physical inspection, not a form. It means walking the building, following the pipes, opening tank lids, checking temperatures, looking at what's actually there.

You're looking for the three conditions that let legionella multiply: warmth (20–45°C), stillness (stagnant water), and nutrients (rust, scale, sediment, biofilm).

A desktop review of drawings and schematics is useful preparation — but it's not the assessment. The assessment happens in the building, with your eyes on the system. L8 ACOP, paragraphs 29–31; HSG274 Part 2, Section 2.1

Review at least every two years. That's the minimum. If something significant changes — new pipework, a change of use, a refurbishment, a legionella detection — review it immediately.

"Significant change" isn't just major construction. A wing closing for summer, a shower block going out of use, a new tenant with different water demand — these all change the risk picture.

The two-year clock is a backstop. A good responsible person is constantly noticing — not waiting for the calendar to tell them to look. L8 ACOP, paragraph 35; HSG274 Part 2, Section 2.1

The risk assessment must be done by a competent person. For a simple system — a small office with a few taps — your trained responsible person may be enough.

For a complex system — a hospital, a care home, a building with cooling towers — you'll likely need specialist help. The complexity of the system determines the competence required.

Even if you bring in an external assessor, the dutyholder still owns the assessment. An expert writes it — you act on it. L8 ACOP, paragraph 25; HSG274 Part 2, Section 2.1

A dead leg is a capped-off branch of pipe. It might be left over from a renovation — a pipe that used to serve a sink that was removed, now capped and forgotten.

Water in a dead leg doesn't move. It sits at ambient temperature, chlorine residual decays, and biofilm builds undisturbed. It's a perfect incubator.

Best fix: remove it. Cut back to the main pipe run. If removal isn't possible, the dead leg must be flushed regularly — but removal is always better. HSG274 Part 2, Section 2.1; L8 ACOP, paragraph 33

Temperature gaps are where hot water cools and cold water warms. Any point in the system where water drifts into the 20–45°C danger zone is a risk.

Look for long pipe runs, poorly insulated sections, cold pipes running next to hot pipes, and outlets far from the heat source where hot water arrives lukewarm.

The rule is simple: cold should stay below 20°C, hot should arrive above 50°C within one minute of running. Anything in between needs attention. HSG274 Part 2, Section 2.3, Table 2.1; L8 ACOP, paragraph 33

Open the lid. Look inside. Is there sediment at the bottom? Is the water clear or discoloured? Is the lid actually tight-fitting, or is there a gap where insects and debris can get in?

Check the insulation. Is the tank in a warm space? Is it insulated to keep heat out? Is the incoming temperature staying below 20°C after storage?

Check turnover. An oversized tank for a building's actual demand means water sits for days. Stale water, decaying disinfectant, rising temperature — all the wrong things happening slowly. HSG274 Part 2, Section 2.3; L8 ACOP, paragraph 33

The shower nobody uses. The basin in the meeting room that's always empty. The tap in the kitchen that people forgot was there. Anywhere water sits because nobody draws it.

Unused outlets are dead legs with a handle. The pipe behind them holds water at ambient temperature, and nobody flushes it through.

Options: flush weekly, remove the outlet, or put it on a scheduled-use rota. A weekly flush log is the most common solution. If an outlet genuinely has no purpose, remove it. HSG274 Part 2, Section 2.3; L8 ACOP, paragraph 33

Who is in your building matters. Legionella doesn't affect everyone equally. Older people, people with weakened immune systems, smokers, and people with chronic lung conditions are at significantly higher risk.

BS 8580 gives a framework for assessing occupant susceptibility. A care home full of elderly residents with respiratory conditions is a fundamentally different risk profile to a warehouse with six healthy staff.

Your risk assessment must account for who's actually there. The same system in the same building has a different risk score depending on who breathes the air. BS 8580-1:2019, Section 6; L8 ACOP, paragraph 30; HSG274 Part 2, Section 2.3

Between 20°C and 45°C, legionella multiplies. This is the danger zone. Below 20°C the bacteria go dormant — they don't die, but they stop growing. Above 50°C they start dying. At 60°C they're killed within minutes. At 70°C, almost instantly.

Your entire control strategy comes down to this: keep cold water cold and hot water hot. The moment either drifts into the middle, conditions favour the bacteria. HSG274 Part 2, Section 2.3, Table 2.1

Moving water is hostile to legionella. Flow brings fresh disinfectant, carries bacteria away, and prevents colonisation. Stagnation does the opposite — it lets bacteria settle, feed, and multiply.

Dead legs, unused outlets, oversized tanks, holiday closures — anywhere water sits without being replaced is a stagnation risk. The fix is always the same: keep it moving. HSG274 Part 2, Sections 2.1, 2.3; L8 ACOP, paragraph 33

Legionella feeds on organic material. Rust, scale, sediment, and biofilm — the thin slimy layer that forms on the inside of pipes and tanks. Biofilm is both food and shelter. It protects bacteria from heat and disinfectant.

Clean systems give bacteria less to work with. Regular tank cleaning, removing sediment, managing scale — these reduce the food supply. You can't eliminate biofilm entirely, but you can starve it. HSG274 Part 2, Section 2.4; L8 ACOP, paragraph 33

The boundary is where the water company's responsibility ends and yours begins. Usually the external stopcock or the point where the service pipe enters your building.

Upstream of the boundary, the water company treats, tests, and delivers. Downstream, it's yours — temperature, quality, distribution, storage, everything.

Know where your boundary is. It's the starting point of your risk assessment — everything you're responsible for flows from that line. HSG274 Part 2, Section 2.1; Water Supply (Water Fittings) Regulations 1999

Mains water arrives at 5–15°C depending on the season — colder in winter, warmer in late summer. That's well below the 20°C growth threshold.

But between the boundary and your first tap, the water passes through pipes — some buried, some in ducts, some running through heated spaces. A cold pipe through a boiler room can arrive at 22°C before it reaches the tank.

Measure the incoming temperature at the point of entry. If it's already above 20°C by the time it reaches storage, you have a pipe route problem to solve before worrying about the tank. HSG274 Part 2, Section 2.3, Table 2.1

The water company adds chlorine to suppress bacteria in transit. By the time it reaches your building, there's a small residual — enough to help, but not enough to rely on.

Chlorine decays. Warm water accelerates the decay. Long pipe runs and storage accelerate it further. In a system with an oversized tank and long distribution, the chlorine residual at the far end can be effectively zero.

That's why temperature is your primary defence, not disinfectant. The chlorine residual is a bonus on arrival — your hot and cold temperature controls are what actually keep legionella suppressed. HSG274 Part 2, Section 2.4; L8 ACOP, paragraph 38

Hard water leaves scale. Soft water causes corrosion. Both create conditions legionella likes. Scale roughens pipe surfaces and gives biofilm more area to attach to. Corrosion produces sediment — food for bacteria.

Your water company publishes chemistry data. Your risk assessment should reference it — knowing what arrives helps you understand what your system is dealing with. Hard area? Expect scale. Soft area? Watch for corrosion.

This is where water quality data meets building safety. The same pipe in a hard-water area and a soft-water area ages differently, corrodes differently, and feeds bacteria differently. HSG274 Part 2, Section 2.4; BS 8580-1:2019, Section 7

An oversized tank is a stagnation risk. If you store 1,000 litres but only use 200 per day, water sits for five days before being replaced — five days of warming, chlorine decay, and bacterial opportunity.

Match tank size to actual demand. A tank that turns over at least once per day keeps water fresh. If the tank was sized for a building that used to have twice the occupancy, it's now too big for its purpose.

If you can't replace the tank, consider a ball valve adjustment to reduce the stored volume, or increase draw-off through scheduled flushing. HSG274 Part 2, Section 2.3; L8 ACOP, paragraph 33

A cold water tank needs a tight-fitting lid. Not resting on top — properly fitted, with no gaps. The lid keeps out dust, insects, bird droppings, and any other organic material that feeds bacteria.

A missing or ill-fitting lid is one of the most common findings in risk assessments. It's a direct contamination pathway — and one of the easiest to fix.

Check that overflow pipes and vent pipes are screened too. An unscreened overflow is an open invitation for insects and debris. HSG274 Part 2, Section 2.3; L8 ACOP, paragraph 33

Turnover is how quickly stored water is replaced by fresh supply. High turnover means fresh water, fresh disinfectant residual, and less time for temperature to drift. Aim for at least once per day.

Watch for short-circuiting. If the inlet and outlet are too close together, fresh water flows straight through while old water sits in the far corners of the tank, untouched. The tank looks busy but pockets of stagnation persist.

Good tank design places the inlet and outlet at opposite ends, forcing water to travel the full length of the tank before being drawn off. HSG274 Part 2, Section 2.3; L8 ACOP, paragraph 33

Insulate the sides and top of a cold water tank. The insulation keeps external heat out. In a heated roof space, an uninsulated tank absorbs warmth and stored water creeps into the danger zone.

Do NOT insulate underneath in a heated space. That seems counterintuitive, but warmth from below should escape downward — insulating the base traps it against the tank, turning the floor into a heat bridge.

Cold pipes running alongside hot pipes need separate insulation. Without it, heat transfers across — a cold pipe touching a hot pipe is a heat bridge. Water that should arrive at 10°C reaches the outlet closer to 25°C. HSG274 Part 2, Section 2.3; L8 ACOP, paragraph 38; BS 8580-1:2019, Section 7