On an industrial site the welfare-block shower is rarely the thing that hurts you. The cooling tower on the roof, the process tank that gets topped up but never fully drained, and the emergency shower nobody has pulled since the last drill — that is where industrial Legionella tends to concentrate. Most water-safety regimes, though, are written for offices, and quietly assume the only systems worth controlling are the hot and cold taps.
So the real question on a factory, warehouse or process plant is not “have we got a logbook”. It is which of your water systems gets which level of attention, and who owns each one. Rank that correctly and almost everything else falls into place.
Why an industrial site is a different problem
A typical office has one water system to worry about: stored and piped hot and cold water feeding taps and a few showers. An industrial site usually has three or four overlapping systems, each with its own way of putting water into the air and its own owner. Cooling towers and evaporative condensers belong to engineering. Process and wash water belongs to production. The welfare block belongs to facilities. The disused line capped off during the last refit belongs, in practice, to nobody.
That fragmentation is the trap. Legionella does not respect the org chart, but your control scheme has to. That is what industrial water safety really turns on: matching each system to a control approach and a named owner. HSE’s guidance on the systems most likely to create risk is a sensible starting list — it puts cooling towers and evaporative condensers near the top precisely because they generate large volumes of fine aerosol [1].
To rank your own systems, judge each on four things: how readily it makes a breathable mist, who is standing in that mist (your workers only, or the public downwind), how warm and still the water gets, and whether a specific legal duty is attached. Those axes — not the diameter of the pipe — decide where your money and attention go.
How the systems compare
| System | Why it bites on an industrial site | How control usually works | The duty people miss |
|---|---|---|---|
| Cooling towers & evaporative condensers | Purpose-built aerosol generators, warm by design, that can carry bacteria beyond the site boundary [3] | A water-treatment programme, scheduled cleaning and disinfection, monitoring — usually with a specialist | Must be notified to the local authority, and they sit among the highest-risk systems on site [2][1] |
| Process & wash water (humidifiers, spray booths, parts and vehicle washers, warm quench or dip tanks) | Often sits in the warm range Legionella favours and sprays directly; frequently left off the water-safety register | Built into the process risk assessment: temperature, turnover, treatment where appropriate | ”It’s not drinking water, so it doesn’t count” — but aerosol is the hazard, not ingestion [3] |
| Welfare hot & cold water (changing-room showers, canteen, toilets) | Shift patterns and PPE mean many showers and taps go little-used; long runs to far buildings | Keep hot hot, cold cold, water moving; flush low-use outlets; clean and descale heads | The low-use outlet problem is worse here than in an office — whole blocks can sit idle for weeks |
| Emergency showers & eyewash stations | Designed to spray, almost never used, so water stands warm and still between tests | Scheduled activation and inspection, logged against the risk assessment | They are a safety asset, so nobody pictures them as a Legionella source |
| Standing or disused water (fire tanks, capped-off lines, idle plant) | Stagnation with no temperature control and no flow | Remove dead legs physically; manage or drain stored tanks | Ownership is unclear, so the line gets capped and forgotten rather than removed |
Where to put the effort first
Read the table top to bottom and you have your priority order. Cooling towers come first every time — not because they are common, but because the mix of large aerosol volume and reach beyond the fence is what turns a site problem into a public-health incident. If you operate one and have never confirmed it is notified to your local authority, that is this week’s job, not next quarter’s.
Process water comes second, and it is the system industrial sites get wrong most often, because it lives outside the plumbing diagram. Walk the floor and list anything that warms water and then sprays, atomises or splashes it: humidifiers, washers, dust-suppression nozzles, warm dip tanks. Each needs a line in the risk assessment even if it never reaches a tap.
Welfare and emergency systems are real risks but more familiar territory, controlled the way you would anywhere — keep the water hot or cold, keep it moving, and don’t let the shower in the rarely-staffed annexe drop off the flushing rota. Stagnation is the thread running through the bottom half of the table, which is why pulling a redundant line out beats flushing it forever; that argument is made in full in on neglected water systems.
A caution before you act
Industrial water systems carry hazards that domestic ones don’t, and the controls can bite back. Cooling-tower disinfection involves biocides and strong chemistry; entering a process or fire tank can mean a confined-space permit and rescue cover; and altering process water chemistry to discourage bacteria can affect the product or the plant. Treat what you have read here as orientation, not a method statement. The actual temperatures, dosing, frequencies and remedial steps come from a competent, site-specific risk assessment — and for cooling towers, almost always from a specialist working to L8 and HSG274 [2][4]. Sampling has its place in verifying or investigating, but how often you sample follows the system and the assessment, not a fixed calendar [5].
The ownership question that decides everything
The single most valuable move on an industrial site is not technical. It is writing down, for every water system on the register, who owns it, what “in control” looks like, and what happens when a reading drifts. “The cooling-tower dip slide is read fortnightly by the treatment contractor; an out-of-range result is reported to the site engineer within 24 hours and triggers a clean” is worth more than any number of generic tasks, because it survives a shift change and a contractor swap. Where readings and exceptions span several owners, a shared digital logbook keeps the record from fragmenting along the same lines the systems already do.
Your next step
Before anything else, build or refresh one asset register that lists every system on site that stores, warms, sprays or stands water — cooling towers and process water included, not just the taps. Against each, name the owner and the control. The gaps in that single table are your real Legionella risks, ranked and ready to act on.
FAQ
Do we have to tell anyone we run a cooling tower or evaporative condenser?
Yes. In the UK these systems must be notified to the local authority, and they also rank among the systems most likely to create Legionella risk, so they draw close attention if anything goes wrong [2][1]. Confirm your notification is current and that the unit appears in the risk assessment with a named owner and a live treatment regime.
Our process water isn’t for drinking — does it still fall under Legionella control?
It can. Legionella is breathed in, not swallowed, so any process or wash water that warms up and then sprays or atomises is a potential source whether or not it is potable [3]. If it makes a mist and sits in the warm range bacteria favour, it belongs in the risk assessment alongside the taps.
Half our welfare showers are barely used because of shift patterns — is that a problem?
It is one of the more common industrial weak points. Outlets that sit unused let warm water stagnate, then aerosolise it the moment someone finally uses them. Either keep them on a flushing schedule sized by the risk assessment, or take genuinely redundant ones out altogether rather than leaving them capped and forgotten.
Sources
[1] HSE, “Systems most likely to create legionella risk”. https://www.hse.gov.uk/legionnaires/risk-systems.htm [2] HSE, “Other duties: RIDDOR and notification of cooling towers or evaporative condensers”. https://www.hse.gov.uk/legionnaires/what-you-must-do/duties.htm [3] CDC, “How Legionella Spreads”. https://www.cdc.gov/legionella/causes/index.html [4] HSE, “Legionnaires’ disease: Technical guidance (HSG274)”. https://www.hse.gov.uk/pubns/books/hsg274.htm [5] HSE, “Testing and monitoring your water system for legionella”. https://www.hse.gov.uk/legionnaires/testing-monitoring-water-system.htm