The fountain in a reception or atrium reads as decoration, not plant. That is exactly the problem. Strip away the slate, the pebbles and the underwater lighting and what you actually have is a tank of warmish water, pumped round in a loop and thrown into the air as fine spray, a few feet from people’s faces. Most of the ingredients Legionella needs, arranged in the spot where the bacteria can reach the most lungs.

Because it looks ornamental rather than mechanical, the feature usually never makes it onto the water risk assessment, the asset register, or anyone’s job description. The danger here is not that fountains are uniquely filthy. It is that they slip through the gap between facilities, grounds staff and whoever installed them, so nobody is actually controlling them.

Why a water feature is almost built to grow Legionella

Run through what a typical recirculating feature does, and it lines up uncomfortably well with the conditions Legionella prefers.

The water moves but never refreshes. A pump keeps the same body of water circulating for weeks, which feels like the opposite of stagnation but isn’t: nothing flushes it out, so anything growing in it simply accumulates. The water tends to sit warm — heat from the pump, from submerged lighting, from a heated atrium, or from summer sun on an outdoor basin can nudge it into the broad 20-45°C band where Legionella multiplies most readily [1]. Then there is the organic load: leaves, dust, coins, dead insects, algae and the skin oils off visitors’ hands all settle in, feeding the biofilm that coats the reservoir and nozzles. Biofilm is where the bacteria shelter.

And then the feature aerosolises the lot. Cascades, jets and fine sprays are designed to break water into droplets — and inhaling contaminated droplets is precisely how Legionnaires’ disease is contracted, not by drinking the water [3]. A spray feature in a busy indoor space is, in effect, a small aerosol generator pointed at passers-by. HSE’s own guidance on which systems create a foreseeable Legionella risk centres on exactly this combination of warm water and dispersal into the air [4].

None of that makes a fountain a guaranteed hazard. It makes it a system that has to be assessed and controlled like any other — which is where the real failure usually lies.

What nobody tells you: the feature nobody owns

Here is the part that catches out even diligent sites. A standard Legionella risk assessment scopes the hot and cold water system: the incoming main, storage tanks, the calorifier, the pipework and the outlets. A decorative feature frequently sits outside all of that. It may be plumbed off a separate top-up supply, or filled by hose. It was installed by a landscaper, an interior fit-out contractor or a specialist water-feature firm — not the plumbing contractor. If anyone maintains it, it tends to be a grounds or cleaning contractor who treats it as a pond to keep clear, not as a Legionella system to keep safe.

So the water-treatment contractor doing your monthly temperature checks never sees it. It produces no log entries. No named person is accountable for it. You end up with one of the highest aerosol-generating systems on site and no owner — which is far more dangerous than a fountain that is merely a bit grubby.

The fix costs nothing and matters more than any chemical dose. Put the feature on the asset register. Name a responsible person for it. Then explicitly pull it into the scope of the water risk assessment as one of the “other risk systems” the duty to assess and control extends to under L8 and the HSG274 technical guidance [1][2]. The duty holder is responsible for identifying and managing every system that creates a foreseeable risk, and “we didn’t think the fountain counted” is not a defence [5]. Done properly — through a competent assessment built on the BS 8580-1 method rather than a quick visual glance [7] — that single step turns an invisible feature into a managed one.

Where the risk actually concentrates

Not every feature carries the same weight. Three patterns are worth picturing.

The indoor lobby or atrium feature — common in offices, hotels, shopping centres and some care settings — is usually the one to worry about most. The water stays warm year-round, the space is busy, and the people walking through can include older visitors and others more vulnerable to infection.

The outdoor ornamental pond or cascade looks lower risk and often is, but don’t write it off. It collects far more debris, and still throws spray that can drift to people nearby or be drawn into a building’s air intake or open windows. Proximity matters more than the indoor/outdoor label.

Then there are the easily forgotten ones: small interior water walls, desktop features and trickling spouts. Low volume, but warm, close to faces, and so minor they vanish from everyone’s radar entirely.

Bringing a feature under control

Once the feature is named and assessed, the practical controls follow the same logic as any water system, adapted to its design. The competent person setting the written scheme should decide which of these apply and how often [1][2]:

  • Decide whether you even need it. The cheapest, most reliable control is removal, or converting a fine-spray design to a non-aerosolising one such as sheet or sheet-over-glass flow with no mist. A feature you don’t run can’t infect anyone.
  • Keep it clean. Remove debris, clean and descale nozzles and the reservoir, and manage the biofilm rather than just skimming the surface.
  • Avoid letting water stew. If the pump runs on a timer, plan for the standing water in between; for features left idle over long periods, drain down rather than leaving warm water sitting.
  • Treat the water where the assessment calls for it, using a competent person and an appropriate regime — not pond products improvised on a whim.
  • Mind the position and the people. Keep spray away from where people congregate and away from air intakes, and add signage where it helps.
  • Monitor as the assessment directs. Sampling can support verification or investigation, but it confirms conditions at one moment and does not replace day-to-day control [6].

One caveat that genuinely matters here: a quiet garden cascade and a misting feature in a packed shopping centre are not the same risk, and the right answer — drain-down intervals, treatment, repositioning, or removing the feature altogether — comes from your own site-specific assessment and the people exposed, not from a rule of thumb. If your feature produces a fine, sustained mist, treat that as a clear step up in concern and get specialist input. This is general guidance, not legal, medical or engineering advice for your installation.

Your first move this week

Walk over to the feature with a notebook and answer four questions. Is it on the asset register? Is a named person responsible for maintaining it? Does it appear anywhere in the water logbook? Does it throw a fine spray near where people stand? If any answer is “no” or “not sure”, you have found your starting point — get the feature written into the risk assessment and give it an owner before you spend a penny on chemistry. The aerosol route that makes these features risky is the same one behind how Legionella spreads through water systems, and the stagnation that feeds them is covered in more depth under neglected water systems.

FAQ

Does a decorative fountain need to be in our Legionella risk assessment?

If it can generate aerosol and hold water in the temperature range Legionella favours, then yes — it is one of the systems a duty holder is expected to identify, assess and control [4][5]. A feature being labelled “decorative” rather than “plumbing” changes nothing about the duty; it only changes how easily the feature gets forgotten.

We drain our fountain every night — is that enough on its own?

Draining down genuinely helps, because it cuts the time water spends warm and still. But it is not a complete answer by itself. Biofilm and scale on the reservoir and nozzles survive a drain-down, the water you refill with may already be warm, and debris keeps accumulating. Pair the drain-down with regular cleaning and whatever treatment and monitoring your assessment specifies.

Is an outdoor water feature lower risk than an indoor one?

Often, but not automatically. Outdoor features still aerosolise water and collect more debris, and spray can drift to people nearby or reach a building’s air intakes and open windows. What matters is how fine the spray is, how warm the water gets, and who is close enough to breathe it — not whether the feature sits inside or out.

Sources

[1] HSE, “Legionnaires’ disease. The control of legionella bacteria in water systems - Approved Code of Practice and guidance (L8)”. https://www.hse.gov.uk/pubns/books/l8.htm [2] HSE, “Legionnaires’ disease: Technical guidance (HSG274)”. https://www.hse.gov.uk/pubns/books/hsg274.htm [3] CDC, “How Legionella Spreads”. https://www.cdc.gov/legionella/causes/index.html [4] HSE, “Systems most likely to create legionella risk”. https://www.hse.gov.uk/legionnaires/risk-systems.htm [5] HSE, “Legionnaires’ disease - what you must do”. https://www.hse.gov.uk/legionnaires/what-you-must-do/index.htm [6] HSE, “Testing and monitoring your water system for legionella”. https://www.hse.gov.uk/legionnaires/testing-monitoring-water-system.htm [7] BSI, “BS 8580-1:2019 - Risk assessments for Legionella control. Code of practice”. https://knowledge.bsigroup.com/products/water-quality-risk-assessments-for-legionella-control-code-of-practice-1