When businesses consider legionella control, the focus is often on obvious water sources such as taps, showers and storage tanks. However, many hidden or lesser-used water systems can also harbour the bacteria, posing a significant risk to health and safety. Neglecting these systems can lead to undetected bacterial growth, increasing the potential for outbreaks. This article highlights some of the most commonly overlooked water systems and outlines how businesses can mitigate the associated risks.
1. Cooling towers and air conditioning systems
If not properly maintained, cooling towers – commonly used in large buildings for air conditioning – can become a major source of airborne legionella bacteria, as the warm, recirculated water within these systems provides an ideal breeding ground. Failure to implement routine maintenance, biocide or copper and silver ionisation treatments and temperature controls, can result in the dissemination of contaminated water droplets into the surrounding environment, posing a risk to building occupants and the public.
2. Spa pools, hot tubs and hydrotherapy baths
Water in spa pools and hot tubs is typically kept at temperatures conducive to legionella growth (between 20°C and 45°C). These systems often generate aerosols, increasing the risk of inhalation exposure and without proper filtration, regular disinfection and effective circulation, they can quickly become breeding grounds for bacteria. Hydrotherapy pools, used in healthcare and rehabilitation settings, require particular attention due to the vulnerability of their users.
3. Misting and humidification systems
Misting systems, used in supermarkets, gyms, and greenhouses, are another frequently neglected source of legionella contamination. The fine water droplets produced by these systems can easily carry bacteria, leading to airborne exposure. Inadequate filtration, lack of regular flushing, and poor temperature control all contribute to the risk. Implementing a scheduled cleaning and disinfection programme is crucial.
4. Decorative water features and fountains
Hotels, corporate buildings and public spaces often feature decorative fountains and water displays. If these systems lack proper water treatment and circulation, they can become stagnant reservoirs for legionella. Regular maintenance, biocide dosing and ensuring consistent water movement are essential to prevent bacterial colonisation. It is also recommended to avoid having decorative fountains in areas that are inhabited by people with a high risk of legionnaires disease, such as healthcare facilities.
5. Sprinkler and fire suppression systems
While fire suppression and sprinkler systems are infrequently used, they can accumulate stagnant water over long periods. When activated, these systems can aerosolise contaminated water, posing an unexpected yet significant health risk. Routine flushing and chlorination during scheduled maintenance can help mitigate the potential hazard.
6. Eyewash stations and emergency showers
Common in industrial settings and laboratories, eyewash stations and emergency showers are designed for safety but can become sources of legionella exposure. If these units are not regularly flushed, stagnant water within the pipes can support bacterial growth. Businesses should implement weekly flushing protocols and periodic disinfection to ensure safe operation.
Why these systems are high-risk
Many of these overlooked systems share common characteristics that make them particularly susceptible to legionella contamination:
- Out of sight, out of mind – They are often not part of routine legionella risk assessments
- Water stagnation – Infrequent use allows bacteria to multiply
- Aerosolisation – Many of these systems create fine water droplets, facilitating the transmission of legionella bacteria through inhalation
Preventative measures for businesses
To reduce the risk of legionella in these hidden water systems, businesses should implement the following best practices:
- Conduct comprehensive legionella risk assessments – Ensure that all potential water sources, including less obvious systems, are evaluated regularly
- Implement routine maintenance and water treatment – Establish schedules for flushing, cleaning and disinfecting all water systems
- Use automated monitoring systems – Smart technology can help track temperature, water flow and bacterial presence, ensuring early detection of risks
- Keep compliance records – Maintain detailed documentation of risk assessments, maintenance activities, and any corrective actions taken
Businesses must recognise that legionella risk extends beyond traditional water systems. By identifying and properly maintaining these commonly overlooked water sources, organisations can prevent outbreaks, ensure regulatory compliance and safeguard public health. Regular assessments, proactive maintenance, and staff awareness are essential components of an effective legionella control strategy.
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