Control of Legionella in Water Systems: A Decarbonised Built Environment Approach

Controlling legionella in building water systems is not only a public health imperative but also an important part of sustainable design. As the UK pursues aggressive carbon-reduction targets (net zero by 2050​), architects and mechanical engineers are rethinking every energy-consuming system in the built environment. One of the largest energy demands in commercial and residential buildings is heating—both for space heating and for hot water supply​. In fact, roughly 17% of an average UK household’s energy use is spent just to heat water​ sunamp.com. This presents a dilemma: traditional methods for controlling legionella (the bacteria behind Legionnaires’ disease) often rely on high water temperatures and other energy-intensive measures, which clashes with decarbonisation goals. The challenge is to ensure safety from legionella in water while minimising carbon footprint.

PearlAqua Kilo - UVC LED Water Disinfection System

Legionella Risks in Building Water Systems

Legionella bacteria are naturally occurring microorganisms found in various water sources. In building plumbing and HVAC systems, they can proliferate under the right conditions and pose a severe health risk. Legionnaires’ disease (sometimes informally called legionnaire disease) is a potentially fatal form of pneumonia caused by inhaling water aerosols containing Legionella​hse.gov.uk. Showers, taps, cooling towers, and decorative fountains can all emit tiny water droplets that carry the bacteria ​hse.gov.uk. Outbreaks of Legionnaires’ disease have been traced to poorly maintained man-made water systems ​who.int​ who.int, since Legionella thrives in the warm, stagnant water that such systems can sometimes provide.

What causes Legionella to grow? The causes of legionella proliferation in water systems are well-understood. Stagnant water and lukewarm temperatures create an ideal breeding ground. The bacteria multiply in water temperatures between 20°C and 45°C, lie dormant below 20°C, and are killed at temperatures above 60°C​ hse.gov.uk. Nutrients and scale in pipes can help form protective slime layers (biofilms) where Legionella bacteria multiply. Such biofilms are particularly troublesome – not only do they harbour bacteria, but they also act as insulators on heat transfer surfaces. Studies show that even a thin biofilm can significantly reduce heat exchanger efficiency (even under 1 mm of biofilm may cause around 30% loss of heat transfer)​. In other words, unchecked bacterial growth not only raises health risks like legionnaire disease in water systems, but also makes heating systems work harder, wasting energy and increasing carbon emissions.

Given the severe health effects and energy impacts, the control of legionella in water systems is tightly regulated. Building operators in the UK are required to assess and manage Legionella risks (per Health and Safety Executive’s ACOP L8 and guidance HSG274). Common recommendations include keeping hot water hot (stored at ≥60°C) and cold water cold (≤20°C) to prevent bacterial growth ​hse.gov.uk, along with regular flushing of seldom-used outlets to avoid stagnation ​hse.gov.uk. While effective for safety, these practices can be energy-intensive – maintaining such temperatures around the clock and routinely flushing water (which then must be reheated) add to a building’s energy use and carbon footprint. This conflict between safety and sustainability drives the search for more sustainable water treatment solutions for Legionella control.

Traditional Methods for Control of Legionella in Water Systems

Building engineers have historically employed a combination of strategies to manage Legionella and prevent Legionnaires’ disease in water systems. Key approaches include:

• Thermal control (high temperatures): Simply put, heat can kill Legionella. Hot water tanks are often kept at or above 60°C and circulated so that even distal outlets stay above 50°C​hse.gov.uk. This temperature regime is effective in controlling Legionella bacteria, but it comes at a cost – heating water to such levels (and keeping it hot continuously) consumes a great deal of energy. In an era of decarbonisation, exclusively relying on high gas or electric heating for safety is less than ideal, as it directly contributes to carbon emissions.

  
  

• Chemical dosing (chlorination and others): Continuous dosing of water with disinfectants (e.g. chlorine, chlorine dioxide) is a common legionella control alternative or supplement to temperature control. While chemicals can be effective at killing Legionella bacteria, they have downsides from a sustainability perspective. Chemicals must be manufactured and regularly transported to site, increasing the carbon footprint of the water treatment. Onsite handling also raises health and safety considerations. Additionally, maintaining the correct residual levels is important – too low and bacteria may survive; too high and the chemicals themselves pose a hazard to users. Chemical treatment is not a very sustainable water treatment solution in the long run due to these ongoing resource and energy costs.

  
  

• Copper-silver ionisation: This method uses electrodes to release copper and silver ions into the water. The ions disrupt microbial cell walls and effectively kill Legionella. Copper-silver systems have been used in some large buildings (like hospitals) for Legionella control. However, they tend to be costly to install and operate, and their sustainability is questionable. Releasing metal ions into the water supply can have environmental impacts (indeed, some countries have banned this technology over ecological concerns​). Over time, the operational expenditure (OPEX) is high, and the approach introduces heavy metals into the water cycle, which is not aligned with green building principles.

  
  

• Ultraviolet sterilisation (traditional UV): Ultraviolet light has long been used to disinfect water. A conventional legionella UV treatment utilises mercury-vapour UV lamps (often emitting at 254 nm UV-C) to inactivate bacteria by damaging their DNA​. UV is a physical, chemical-free process – water passes through a chamber where it is irradiated, killing pathogens like Legionella instantly. This is widely regarded as a clean and effective approach, with minimal residual effect on water quality. In fact, UV is often the most common supplemental disinfection method for Legionella control in buildings, due to its effectiveness and low immediate operating cost. However, traditional UV systems have their own drawbacks:

  

  • The typical mercury-based UV lamp must stay on continuously to avoid warm-up lag and lamp wear from frequent switching. In building water systems with intermittent flow (e.g. peak usage in daytime, very low at night), a standard UV lamp still consumes full power 24/7​. This means a constant energy draw even when no water is flowing, undermining energy-efficiency efforts.

  • If water sits idle around a hot UV lamp, it can heat up the surrounding water. Traditional UV units often experience the lamp heating the water in the chamber to >50°C during stagnation​. When flow resumes, this slug of overly warm water may be sent into the cold water lines, which is undesirable (it not only wastes energy but could also inch the water into the Legionella growth range). To counteract this, many installations add temperature sensors and automated flushing valves that dump overheated water to drain​. While effective, this practice wastes water and energy (as the dumped water was heated for no purpose). In summary, conventional UV units, while excellent at controlling legionella, can inadvertently increase a building’s water and energy wastage – adding to the carbon footprint through continuous electrical use and thermal losses.

Each of the above methods has merits, but also significant environmental or efficiency downsides. To truly decarbonise the built environment without compromising on legionella safety, newer technologies need to address these gaps. This is where recent advances like UV-C LED technology come into play as a more sustainable option.

UV-C LED: Sustainable Water Treatment with LED UV Technology

Recent developments in light-emitting diode (LED) technology have led to compact UV-C LED disinfection systems that can replace traditional mercury lamps. These LED UV systems produce the same germicidal UV-C light but with solid-state semiconductors instead of fragile glass bulbs. For Legionella UV applications, UV-C LEDs offer several key advantages supporting sustainability and energy efficiency:

• On-demand operation: UV-C LEDs can turn on at full intensity almost instantly, and can cycle on/off frequently without degradation. This means a UV-C LED water purification unit can be set to activate only when water flows, or in periodic pulses during no-flow conditions, dramatically cutting energy usage. By contrast, a mercury lamp must stay on continuously at 100% power​. LED units eliminate the needless 24/7 power draw. The result is that energy consumption drops to only what’s needed for actual water treatment, supporting the building’s decarbonisation goals by reducing electrical waste.

  
  

• Cool operation & no overheated water: LEDs run cooler than mercury lamps and are often arranged around the outside of the flow, so they don’t heat the water significantly. They also can be switched fully off when idle, so there is no constant hot surface warming up stagnant water. This removes the need for wasteful flushing of hot water down the drain. Overall, LED UV systems avoid the unintended heating of water, thereby conserving both water and energy.

  
  

• Longer practical lifespan: A modern UV-C LED module has a lifespan comparable in hours to a mercury lamp (often around 8,000–10,000 hours). However, because an LED is off much of the time in intermittent use, the calendar life of LED modules can be much longer – potentially several years before replacement is needed. Fewer replacement cycles means less waste and lower maintenance resources over the system’s life, aligning with sustainability objectives.

  
  

• No toxic materials: Traditional UV lamps contain mercury, a toxic heavy metal. Handling and disposing of mercury lamps pose environmental hazards. In fact, the Minamata Convention (a UN environmental agreement) has prompted countries to phase down mercury use to protect health and the environment. UV-C LED devices are mercury-free, which avoids introducing this persistent pollutant into the building or waste stream​. This supports both environmental safety and future-proof compliance with emerging regulations restricting mercury. In short, LED UV is a sustainable water treatment solution that is inherently cleaner.

  
  

• Smart control and integration: LED UV systems can be equipped with smart controllers to modulate output based on flow rate or water quality. For example, power can ramp up for high flow or slightly turbid water and dial down for low flow or clear water, ensuring an appropriate UV dose with minimal energy use​. They can also interface with building management systems, providing data on performance and allowing integration into the facility’s overall energy optimisation strategies (further contributing to efficient operation in the built environment context).

By leveraging these advantages, UV-C LED technology provides sustainable water treatment solutions that maintain the control of legionella in water systems without the energy penalties of older methods. It effectively addresses both sides of the challenge: safeguarding public health and reducing carbon footprint.

UV-C LED Solutions for Legionella Control in the Built Environment

To illustrate how this technology is being applied, consider the PearlAqua range of UV-C LED water purification systems (from LED UV-C Systems Ltd). These systems demonstrate the scalability and adaptability of LED UV for different use cases in the built environment:

• PearlAqua Micro: A ultra-compact point-of-use UV-C LED disinfection device. The Micro can be installed directly at taps, showers, or medical outlets to provide final barrier protection against legionella bacteria and other pathogens at the point of delivery. This is particularly useful in healthcare settings (e.g. hospitals or care homes) where controlling legionella at faucets and showers is critical for vulnerable users. The PearlAqua Micro’s small size has even enabled its use in unique applications like ensuring safe water on spacecraft and airplanes, proving its versatility in delivering LED UV disinfection wherever needed.

  
  

• PearlAqua Deca: A mid-sized point-of-entry UV-C LED system designed for whole-house or small facility water treatment. The Deca is typically installed on a building’s incoming water supply (for example, in a commercial office, school, or a large home) to treat all water flowing into the premises. It’s often employed in facilities that rely on private water sources, such as boreholes or rainwater harvesting systems, to ensure these alternative water supplies are free of Legionella and other microbes. By using a legionella UV treatment at the point-of-entry, building owners can reduce reliance on maintaining extreme water temperatures or chemical dosing, thereby improving energy efficiency and water quality in one step.

  
  

• PearlAqua Kilo: A larger UV-C LED system built for high flow rates (handling approximately 20–230 m³/h). The PearlAqua Kilo is ideal for control of legionella in water systems serving big commercial buildings, campuses, hotels, and hospitals. It can be installed after a central cold-water storage tank or integrated into the main water circulation loop to continuously disinfect large volumes of water supplying multiple outlets. This scale of LED UV unit brings the benefits of on-demand, mercury-free disinfection to the core of a facility’s water system. By doing so, even very large buildings can avoid the carbon cost of keeping thousands of litres of water superheated, without compromising on safety. The PearlAqua Kilo exemplifies how UV-C LED water purification can dovetail with energy-efficient building design – providing a balanced solution of clean water and intelligent energy use.

Each of these examples shows how UV-C LED systems can be tailored to different scales in the built environment, from a single tap to an entire skyscraper. They offer building engineers and facility managers new tools to control legionella proactively, often allowing for lower hot water setpoints or reduced chemical use, which in turn yields energy savings and carbon reductions.

Decarbonisation and Legionella Safety Hand-in-Hand

In today’s building design, the goals of public health protection and carbon reduction must go hand-in-hand. Achieving a decarbonised built environment means rethinking old assumptions about how we heat and treat water. Efficient control of legionella in water systems can no longer be seen as separate from energy efficiency – the two are deeply interlinked. By adopting modern solutions like UV-C LED water purification units, building operators can prevent Legionnaires’ disease while also cutting energy waste associated with traditional methods. This dual benefit is crucial as we strive for buildings that are both safe for occupants and sustainable for the planet.

In summary, Legionella UV disinfection using advanced LED technology represents a leap forward in sustainable building services. These systems provide robust protection against the causes of legionella growth without the significant carbon footprint of previous approaches. With governmental pressure on buildings to become greener and meet net-zero targets, innovations like LED UV enable us to maintain water hygiene standards decarbonisation of the built environment. By implementing these sustainable water treatment solutions, we can ensure that the drive to save energy and reduce emissions never compromises the vital control of legionella and the health of building occupants.

Ready to Future-Proof Your Building Water System?

Whether you're designing a new facility or upgrading an existing one, LED UV-C Systems Ltd. can help you achieve both Legionella control and decarbonisation with advanced UV-C LED water purification technology. Our team is here to help you select the right solution—from point-of-use to high-flow systems like the Micro, Deca, and Kilo—tailored to your building's needs.

Let’s make safe, sustainable water treatment the standard in the built environment.

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