Legionella in cooling towers: The overlooked threat behind healthcare outbreaks

The recent Legionnaires’ outbreak in New York City, traced to cooling towers at Harlem Hospital, shows how even advanced facilities can become carriers of Legionella. 

Legionella bacteria thrive in stagnant water and spread through aerosols from showers, faucets, and cooling towers, posing serious risks in healthcare environments.

For healthcare engineers, plumbers, and facility managers, this isn’t just a mechanical issue. Legionella in cooling towers is a healthcare water safety challenge that requires certified, multilayered protection.

Why are cooling towers high-risk for Legionella in hospitals?

Cooling towers, part of HVAC systems, continuously cycle warm water to regulate temperature, conditions ideal for Legionella growth.

When contaminated droplets are released, aerosols can drift into patient areas through ventilation, turning HVAC systems into transmission pathways. 

Hospitals face a higher risk due to complex water networks and vulnerable patients. Even when potable water meets safety standards, Legionella can multiply in cooling towers, spreading invisibly through mist and ventilation.

How does ultrafiltration prevent Legionella in cooling towers?

Ultrafiltration is an advanced water treatment process that uses semi-permeable membranes to physically remove microorganisms and suspended particles from water.

Mentor Water’s ultrafiltration uses hollow-fiber membranes with pore sizes around 0.08 µm, small enough to capture bacteria, fungi, and other pathogens while allowing water molecules to pass through.

Unlike chemical disinfection, ultrafiltration provides a physical barrier that achieves Log 8 (99.999999%) reduction in microbes, ensuring consistent protection even when water quality fluctuates.

How can healthcare facilities prevent Legionella through layered protection?

Effective Legionella control in healthcare requires multiple barriers. Each water system component, from cooling towers to faucet outlets, must be treated as a potential contamination point.

• Cooling towers: Regular monitoring, maintenance, and certified filtration prevent bacterial growth.

• HVAC integration: Ensuring clean water reduces the risk of airborne spread through ventilation.

• Point-of-entry systems: Filtering incoming water prevents contamination from seeding towers and distribution lines.

• Point-of-use (POU) systems: Protection at the outlets for patients and staff, ensuring safe water delivery even if contamination occurs downstream of the POE.

When hospitals rely on certified filtration solutions at the Point-of-entry systems, it provides an important first barrier of protection, reducing microbial load as water enters the hospital. 

But once water passes through cooling towers, hot water distribution, and plumbing networks, it can still become contaminated with Legionella and other pathogens. That’s why Point-of-Use (POU) filters in healthcare are essential to complete the protection that POE starts.

This layered defense aligns with ASHRAE 188 and Guideline 12 recommendations, protecting patients, staff, and surrounding communities from Legionella outbreaks.

Mentor Water’s certified healthcare filtration systems for Legionella prevention

Disinfection methods like chlorination or UV reduce microbial loads, but they cannot guarantee downstream protection if bacteria recolonize in plumbing or cooling systems. Certified ultrafiltration provides a physical barrier, ensuring water safety where patients use it.

• Showers: PurGuard360® handheld system for high-risk areas such as oncology wards, burn centers, and long-term care, protecting patients from aerosolized Legionella.

• Faucets: TapTech Pro® filters for surgical preparation zones, patient rooms, and food service outlets, ensuring safe water for handwashing and hygiene.

• Inline & POE protection:  Inline PureFlow®, AquaGuard Pro®, and TotalPure® systems protect ice machines, beverage lines, laboratories, and entire building networks, ensuring safe water delivery even if contamination occurs after the main POE.

Mentor Water’s filtration solutions, produced in an EPA FIFRA-registered establishment (EPA Est. No. 105402-NLD-1), are engineered specifically for healthcare, certified to NSF P376, ASSE 2011-2022, ASTM F838-2020, and EPA WaterSense®. 

CE marked, they are also compliant with the EU Drinking Water Directive (2020/2184) and EN-16421 standards. By combining POE and POU protection, Mentor Water ensures safe water delivery even if pathogens develop inside cooling towers or distribution systems. 

Certified filtration: The smartest defense against complex waterborne risks

The Harlem Hospital outbreak shows cooling towers remain an overlooked Legionella source. Point-of-entry filtration is essential, but only point-of-use systems ensure safety where patients use water.

Each Mentor Water Technologies solution is engineered not just to react after contamination occurs, but to prevent infection before it begins.

Learn more about Mentor Water’s healthcare filtration solutions or contact the Mentor Water Technologies team for a technical consultation.