From cooling towers to splash pads – Staying safe while keeping cool

As climate change drives more frequent and intense heat events, the risk of heat-related illness and death is rising globally. In response, many cities are developing urban cooling strategies that include expanded access to air-conditioned indoor spaces or outdoor water-based cooling solutions like misting stations, splash pads, and pools. As the need for cooling grows, it is important to be aware of some of the microbiological hazards that cooling solutions can present. This blog provides an overview of some of those hazards, and signposts to resources and guidance for reducing exposure and preventing infection while keeping people cool.

Pathogens linked to cooling infrastructure

Both opportunistic and enteric pathogens can be present in cooling infrastructure (Table 1). Opportunistic pathogens (e.g., Legionella spp., Mycobacterium spp., Pseudomonas spp.,) occur naturally in the environment but they can grow and propagate in engineered water systems like premise plumbing, cooling towers, water misting devices, pools, and water storage tanks. Enteric waterborne pathogens (e.g., Cryptosporidium spp., Escherichia coli, Norovirus), in contrast, originate in human or animal feces, and may enter recreational water venues directly via the water users or indirectly via runoff from contaminated surfaces.

While sources of exposure and health outcomes vary, some common risk factors for the growth and persistence of these pathogens in cooling infrastructure include:

• Untreated or poorly treated recirculated water.
• Loss of disinfectant residual, exacerbated by warm temperatures, stagnation, aerosolization, and organic contamination.
• Biofilm formation, which can shield pathogens from disinfectants.
• Warm water that remains > 25°C, optimal for pathogen survival and growth. Many opportunistic pathogens thrive in hot and humid conditions.

Table 1. Examples of pathogens that may be present in cooling infrastructure

Aerosols, air conditioning, and Legionella

Cooling towers, recreational water venues, decorative water features, and other systems that produce mists or aerosols can be sources of Legionella exposure. Of these, evaporative cooling towers in large, air-conditioned buildings, malls, hospitals, and hotels have been the source of large Legionnaires’ disease outbreaks and accounted for most outbreak-associated deaths. Cooling towers work as heat exchangers, spraying water over pipes or coils, which evaporates and dissipates heat to the atmosphere assisted by fans or blowers. If cooling tower water is colonized by Legionella, the bacteria can become entrained in aerosols and spread across urban areas causing infections.

Reported cases of legionellosis have increased in many industrial countries in recent decades. Reporting in South Korea and Belgium has suggested a link between climate warming, increased cooling tower use, and cases of Legionnaires’ disease. Calls for heightened awareness and preparedness for a rise in Legionnaires’ disease emphasize the need to improve control measures and surveillance to identify and contain outbreaks early.

Less is known about the risk of infection caused by opportunistic pathogens in water misting stations; however, opportunistic pathogens like Legionella can potentially colonize any engineered water systems under the right conditions. One Australian study detected opportunistic pathogens in over two-thirds of samples collected from water mist systems used for cooling. Positive detections of Legionella and Pseudomonas were associated with elevated solids and organic carbon in the water, and the presence of biofilms. This highlights the importance of maintaining systems in good condition to limit pathogen growth.

Splash pads, bacteria, and brain-eating amoeba

Splash pads are water parks with interactive features like jets and fountains, particularly popular for keeping younger children and toddlers cool. Systems can either be single-pass, draining water away from surfaces directly to sewer, or recirculating systems, collecting water in storage tanks for treatment and recirculation back into the water features. Recirculating systems present a much higher infection risk if treatment is poorly designed or maintained, or filtration and disinfection systems fail.

The US CDC reported that splashpads caused over 10,000 waterborne illnesses between 1997 and 2022, with Cryptosporidium spp. from fecal contamination responsible for most outbreaks. Feces can enter the splash pad water via leaky diapers or park users sitting or standing on sprays. Children are at the greatest risk of infection due to behaviours such as putting their mouths on or near jets or sprays and ingesting water during play.

Infections with the opportunistic pathogens on splash pads are not as frequent as those caused by enteric pathogens and children are less susceptible to infections like legionellosis. Infections caused by organisms like Mycobacteria spp. and Pseudomonas spp. are non-reportable, so incidence is not fully understood; however, people suffering from conditions like cystic fibrosis are at higher risk.

Rarely, infections with Naegleria fowleri have been linked to splash pads in the United States. Infection occurs via forceful injection of contaminated water directly up the nose, which can occur via water jets or sprays. N. fowleri is sometimes referred to as the brain-eating amoeba, as nasal injection allows the pathogen to reach the brain, where it causes potentially fatal primary amoebic meningoencephalitis (PAM). Splash-pad associated deaths due to N. fowleri infection have occurred in young children. The death of a three-year-old child in Arlington, Texas in 2021 led to the development of the Bakari Williams Protocol for safe operation of pools and splashpads. There have been no known infections with N. fowleri ever reported in Canada; however, a warming climate could expand the northern range of this naturally occurring organism.

Preventing exposure and reducing infection risks

Although well-established guidance exists for managing microbiological risks in cooling towers and recreational water venues, significant outbreaks of legionellosis and outbreaks associated with treated recreational water venues continue to occur. As the density and usage of cooling infrastructure increases, so will exposure and infection risks if not managed properly. Renewed awareness of risks and revised strategies for protecting susceptible people from infection are needed.

• For cooling towers: There is a need to refresh building water management plans and review the sampling, maintenance and operation protocols needed to prevent growth and exposure to Legionella. Risk reducing measures can include:
  • Keeping cooling tower water clean by maintaining disinfection, preventing the accumulation of organic contaminants, and preventing conditions that favour biofilm or bacterial growth.
  • Monitoring cooling tower water for parameters like solids, organic carbon, chlorine residual and Legionella to identify problems before they occur and take corrective action.
  • Using cooling tower registries to set testing and maintenance criteria and help identify sources of outbreaks more quickly (e.g., as used in Hamilton, ON, Vancouver, BC, New Brunswick and Quebec).
  • Improve awareness of conditions that increase the risk of legionellosis outbreaks, and outbreak patterns and lag times associated with various environmental conditions (e.g., rainfall, high humidity, storms).
     
• For splash pads or wading pools: There is a need to continue to apply control measures based on local guidelines and regulation. Risk reducing measures can include:
  • Use single-pass systems where possible, to avoid the hazards that can arise in recirculating systems. Consider advising users whether the system is a single-pass or recirculating one.
  • Maintain splash pad or pool surfaces to reduce accumulation of dirt, debris, or feces that can present a direct infection risk, deplete chlorine residual, or encourage biofilm growth. Do not drain wash water to recirculating tanks.
  • For recirculating systems, ensure the use of secondary disinfection such as UV light or ozone, and ensure adequate maintenance of the treatment system.
  • Carry out regular inspections of surfaces, storage tanks, and treatment systems including filtration, pH adjustment and disinfection, and test for chlorine residuals regularly, particularly during peak times.
  • Increase awareness of hazards by posting signage on hygiene and safe behaviours (e.g., do not drink water or jet it into the mouth/nose; don’t eat or drink at the poolside; wash hands with soap and tap water before eating).
  • Emphasize key messages that prevent fecal contamination such as not using the water when experiencing nausea, vomiting, or diarrhea, showering before entry, and not rinsing diapers on splash pad surfaces.
     
• For other blue infrastructure like misters, irrigation, and decorative features, consider the protocols that are needed to limit infection risks. This is necessary for features that are conducive to pathogen or biofilm growth AND have the potential to expose the public to aerosols. Risk reducing measures could include:
  • Regularly cleaning spray heads and nozzles to prevent biofilm growth
  • Prevent pathogen growth in stored water (if used) by keeping itcool, maintaining a disinfectant residual (if appropriate), and cleaning out tanks periodically.
  • Limit the release of aerosols where possible by timing usage (e.g., irrigating in the early morning, evening, in calm weather) or adjusting delivery mechanism (e.g., drip irrigation) to limit aerosol generation.

By being proactive and recognizing that cooling infrastructure can pose some public health hazards, cooling strategies can be designed to ensure that people are protected from the heat while safeguarding against unintended infection risks.

Further resources and guidance

Legionella and opportunistic pathogens

• Pathogen safety data sheets (Public Health Agency of Canada, 2025)
• Controlling Legionella (US CDC, 2025)
• A review of Legionella transmission risk in built environments: sources, regulations, sampling, and detection (Yao et al. 2024)
• Legionella (NCCEH Subject guide, 2022)
• Climate change and opportunistic pathogens (OPs) in the built environment (NCCEH, 2022)

Splash pads and treated water venues

• What you can do to stay healthy at splash pads (US CDC, 2025)
• Recreational water reference document (Ontario Ministry of Health, 2025)
• Model Aquatic Health Code (US CDC, 2024)
• Preventing the spread of germs in splash pads: A quick guide for health departments and operators (National Association of Country and City Health Officials, 2023)
• Naegleria fowleri and public water systems (US CDC, 2025)
• Pools, hot tubs, and other treated recreational water venues (NCCEH Subject guide, 2022)
• Identifying and addressing the public health risks of splash parks (NCCEH, 2017)