Why Cooling Towers in Data Centres Need More Than Just Chemicals

Categories: Armour, Armour X, Blog, Commercial, Data Centre, GMP-Series, MPX-Series, WF-Series

A data centre that overheats goes offline. That single fact puts cooling infrastructure at the very top of any facility manager’s priority list. But here’s the part that often gets overlooked: the water running through your cooling towers and recirculating systems is just as critical as the hardware it protects.

Biofouling, Legionella risk, scale build-up, and corrosion don’t send an alert to your monitoring dashboard. They build slowly, quietly eroding heat transfer efficiency, shortening equipment life, and creating compliance exposure. By the time the problem is visible, the damage is already done.

This article looks at the specific water treatment challenges facing data centre cooling systems, where UV disinfection fits within a compliant treatment programme, and how facilities teams are using it to strengthen what chemicals alone cannot cover.

Cooling towers are, by design, ideal environments for microbial growth. They’re warm, wet, and continuously cycling water through a process that concentrates dissolved solids with every evaporation cycle. If your water treatment programme isn’t actively controlling biofilm, you’re operating on borrowed time.

The three most common problems that facilities teams encounter are:

• Legionella pneumophila: the bacterium responsible for Legionnaires’ disease thrives in the 20 to 45°C range, which is precisely where cooling tower water sits. Outbreaks are rare but devastating, both in human cost and reputational damage. Regulatory requirements around Legionella control are tightening across Australia, the UK, the US, and the EU.
• Biofilm and biofouling: a thin, persistent layer of microorganisms coating your pipes and heat exchange surfaces reduces thermal efficiency and creates a reservoir for Legionella and other pathogens. Controlling biofilm requires chemical treatment; it cannot be addressed by UV alone, as UV only acts on water passing through the system at that point.
• Scale and corrosion: biological activity accelerates electrochemical corrosion, particularly in the presence of sulphate-reducing bacteria. Left unchecked, this leads to pipe failures, leaks, and costly unplanned maintenance.

A hyperscale operator in the UK had chemical dosing running to schedule, yet still experienced a biofilm-driven efficiency drop across two cooling towers, adding approximately 8% to cooling energy costs over a single summer. The issue wasn’t the chemicals. It was that chemicals alone couldn’t hold the line against makeup water bringing in continuous microbial loading.

Chemical treatment in cooling loops is not optional. In most jurisdictions it is mandated as part of a Legionella risk management programme, and for good reason: chemicals provide the residual disinfection that keeps water safe between treatment cycles and within the system itself. UV cannot replicate this. What UV does is address the limitations of chemicals at specific points in the system, particularly at the point of makeup water entry.

• Resistance: over time, microbial populations can develop tolerance to biocides, particularly oxidising agents like chlorine. Rotating chemicals helps, but adds programme complexity and cost. UV works through a physical process that microorganisms cannot build resistance to.
• Makeup water loading: incoming mains or harvested water can carry a significant microbial load before it ever enters the cooling circuit. Treating this water with UV at the point of entry reduces the overall burden on the chemical programme, allowing it to work more effectively on residual control.
• Environmental and safety burden: chemical storage, handling, and blowdown disposal requirements are increasing under environmental regulations. For facilities with Green Star ratings, LEED certification, or internal ESG commitments, reducing chemical volumes where possible is increasingly non-negotiable.
• Operational cost: where UV reduces the microbial load entering the system, the chemical programme can often be maintained at lower dosing concentrations, reducing procurement costs without compromising compliance.

The result of a well-designed programme is that UV handles point-of-entry disinfection, chemicals handle residual protection and system-wide control, and silver ionisation can provide an additional residual layer where appropriate. Each technology does what it does best.

UV-C light at 254 nanometres disrupts the DNA and RNA of microorganisms, preventing them from reproducing. It’s a physical process, not a chemical one. There’s no residual in the water, no handling risk, and no discharge concern.

It’s important to understand what UV does and doesn’t do in a cooling application. UV sterilises the water passing through the chamber at that point in the pipe. It does not provide residual disinfection in the loop, it cannot penetrate established biofilm on pipe surfaces, and it does not replace the chemical programme required under Legionella control regulations. What it does is significantly reduce the microbial load at the point of treatment, which is most valuable at the makeup water entry point.

In a data centre context, UV is most commonly deployed for:

• Makeup water treatment: treating incoming mains or harvested water before it enters the cooling circuit. This is where UV delivers the clearest, most measurable benefit, reducing the volume of microorganisms entering the system before the chemical programme takes over.
• Water reuse applications: UV is a core technology in rainwater harvesting and greywater reuse systems within the data centre site, enabling safe non-potable water use for applications such as toilet flushing and irrigation.

UV Guard’s Melbourne data centre case study is a practical example of this broader application. A newly developed facility required a compact, automated UV disinfection system to enable safe reuse of harvested rainwater for non-potable purposes within the site. The solution needed to be reliable and low-maintenance given the critical nature of the facility, and it has performed to specification since installation.

Not all UV systems are designed for the demands of a commercial or industrial cooling circuit. Flow rates, water quality variations, and the need for monitoring and alarm outputs all need to be factored into the specification.

Getting the specification right from the start matters. The wrong system size, the wrong placement, or a mismatch between UV transmittance requirements and actual water quality can undermine the whole treatment programme. This is where the UV Guard team’s experience becomes practical rather than just theoretical.

UV Guard works alongside operational teams and engineering consultants from initial site assessment through to system selection, installation support, and ongoing after-sales service. For data centre projects in particular, where uptime expectations are absolute and the consequences of getting it wrong are significant, that continuity of technical support is something clients come back to every time.

The conversation typically starts with understanding the existing cooling infrastructure, water source and quality, flow rates, and current treatment programme. From there, the right system becomes a straightforward recommendation rather than a guessing game.

Data centre projects often involve multiple stakeholders: the facilities team, the water treatment consultant, the M&E contractor, and sometimes the base building engineer. UV Guard’s team is experienced in working across all of those relationships, providing the technical data each party needs at each stage of the project.

The current UV Guard range suited to data centre cooling water treatment covers moderate through to large commercial and industrial flow rates:

Armour

The Armour series is a proven commercial UV system suited to moderate-flow applications including makeup water treatment for smaller cooling tower circuits. It’s a practical, cost-effective entry point for facilities introducing UV to their water management programme.

Armour X

For larger flow requirements, the Armour X delivers compact, high-output UV disinfection with even dose distribution and low pressure drop. It’s designed for liquids with lower UV transmittance values and high-dose requirements, making it suitable for recirculating cooling water that may carry elevated suspended solids.

AQ Silver Ionisation

For applications requiring residual disinfection, the AQ Silver Ionisation system is worth serious consideration. Silver ionisation is one of the few technologies, alongside chlorine, that provides residual protection in the water loop. Silver ions remain active after the point of treatment, continuing to control bacterial growth over time. This makes it particularly relevant for cooling tower applications where residual control is a compliance requirement. UV and silver ionisation are increasingly being specified together, with UV handling point-of-entry load reduction and silver providing the ongoing residual protection in the circuit.

GMP Series

The GMP Series is designed to high regulatory standards and is suited to applications where validated, auditable performance is required. For data centres operating under strict compliance frameworks, the GMP Series provides the performance documentation to support those requirements.

MPX Series

The MPX Series is UV Guard’s large-scale industrial system, suited to high-volume recirculating water treatment in hyperscale and enterprise data centre environments where flow rates are significant and continuous uptime is expected.

WF Series

The WF Series is a mechanical bag filtration system. While not a UV or disinfection product, pre-filtration is often a necessary part of a water treatment setup, particularly where incoming water carries suspended solids that could reduce UV transmittance. It is worth discussing with the UV Guard team whether filtration should be part of the overall specification for your site.

Data centres are responsible for a significant share of global water and energy consumption. The pressure from investors, regulators, and corporate sustainability teams to address this is real and growing.

UV disinfection supports sustainability objectives in several concrete ways:

• Reduced chemical discharge: less reliance on chemical biocides means less chemical blowdown entering the stormwater or sewer system.
• Water reuse enablement: UV is a core technology in rainwater harvesting and greywater reuse systems, reducing mains water consumption.
• Lower energy footprint: clean heat exchange surfaces maintained through effective water treatment allow cooling systems to run more efficiently, directly reducing energy consumption.
• Regulatory alignment: meeting water quality and Legionella control requirements proactively reduces the risk of enforcement action and associated reputational damage.

In Australia, AS/NZS 3666 sets out obligations for the control of microbial growth in air-handling and water systems. Across the UK, the HSE’s Approved Code of Practice L8 sets the standard for Legionella control. Both frameworks increasingly support the use of UV as part of a validated risk management programme.

Every cooling system is different. Flow rates, water quality, existing treatment programmes, and compliance obligations all affect the right specification. UV Guard’s technical team works directly with facilities managers, engineers, and water treatment consultants to design solutions that fit the specific demands of each site.

To explore the full range of data centre cooling applications or to speak with a specialist, visit uvguard.com or call +61 2 9631 4900.