In healthcare facilities, the greatest Legionella risk isn’t just in the cooling towers, or air conditioning systems. It’s in the water patients use every day. From domestic hot water tanks and showers to handwashing sinks and ice machines as well as air conditioning systems, the very facilities designed to support patient care can, under certain conditions, become pathways for disease. For hospitals, outpatient clinics, and long-term care homes, Legionella control is a frontline responsibility.

As part of EAI’s “The Water Industry is All Industry” campaign, this article explores how Legionella control in healthcare must be integrated into daily operations. We’ll walk through effective control measures, review vulnerable plumbing designs, and show how a comprehensive water management program can prevent Legionella growth, protect high-risk individuals, and keep facilities compliant with the latest public health standards.

Legionella and Why Healthcare Potable Water Systems Are at Risk

Legionella is a waterborne bacterium naturally found in freshwater environments like lakes and streams, but it becomes dangerous when introduced into complex built environments such as healthcare facilities. Once it enters domestic hot water or cold water loops, sinks, showers, tanks, or humidifiers, Legionella can thrive under certain conditions and spread through the air via aerosolized droplets.

Inhalation is the most common transmission route, making even routine activities like showering a potential source of Legionella exposure. The most severe form of illness, Legionnaires’ disease, is a type of pneumonia that disproportionately affects vulnerable patients. Pontiac fever, a milder flu-like illness, is also caused by Legionella growth and exposure.

Healthcare water distribution systems are especially vulnerable due to their complexity and the sensitivity of the patient population. Legionella pneumophila, the most dangerous strain, is adept at colonizing biofilms, resisting common disinfectants, and persisting in warm water environments. It is classified among opportunistic pathogens, organisms that don’t typically infect healthy people but can cause severe illness in those with compromised immune systems.

Without active control measures in place, even well-designed systems can harbor Legionella. Fluctuating temperatures, stagnant water flow, or aging distribution systems allow bacteria to bypass standard protections, making proactive monitoring and control essential.

Key Control Challenges for Legionella in Healthcare Potable Water Systems

Even modern healthcare buildings can harbor conditions that support Legionella growth and legionnaires disease outbreaks. Identifying and managing these control challenges is critical for any water supply system. Below are the most common and actionable factors that compromise Legionella control in domestic hot and cold water distribution systems:

1. Suboptimal Hot Water Temperatures and Equipment

Hot water tanks or distribution systems that operate below 120°F (49°C) can inadvertently support Legionella bacteria proliferation. While temperature limits are often implemented to prevent scalding in patient care settings, this creates a “danger zone” between 68°F and 113°F (20–45°C), ideal for bacterial growth. Facilities must balance disinfection and safety using thermostatic mixing valves, visual inspections, and routine documentation at points of use.

2. Infrequently Used Outlets and Cold Water Stagnation

In hospitals and large clinics, certain sinks, showers, fire protection systems, or therapy tubs may only be used seasonally or during specific procedures. These low-use fixtures allow both hot and cold water to stagnate, creating prime conditions for biofilm and Legionella colonization. Pumps that are not properly cycled can contribute to stagnant zones within distribution systems, especially on the top floor or in remote wings with lower pressure and intermittent water flow, leading to increased risk.

3. Aging Infrastructure and Corrosion

Even in updated facilities, aging plumbing infrastructure can hide unseen risks. Corroded fittings, scale buildup, and degraded materials provide surface area for biofilms to anchor and protect Legionella from disinfectants. Corrosion also disrupts water flow and temperature consistency. EAI has encountered high-risk areas where older pipes, poorly insulated tanks, or air conditioning units contributed to inconsistent temperatures and increased bacterial persistence.

4. Neglected or Improperly Maintained Filtration Systems

Point-of-use and central filtration systems must be designed and maintained to prevent microbial contamination, not contribute to it. Filters past their service life or those not rated for microbial reduction (e.g., NSF/ANSI 53 or 58) can become unintended breeding grounds. Water supply systems must ensure filters are appropriate for healthcare applications and tracked as part of routine maintenance and control measures.

5. Dead Legs, Loop Stagnation, and Poor Hydraulic Design

Dead-end piping or poorly designed recirculation loops within distribution systems are silent risks. When pumps fail to maintain circulation or design flaws trap water in dead legs, disinfection residuals drop, and bacteria gain a foothold. Distribution systems that lack flow-balancing valves or exhibit pressure differentials across floors (particularly lower pressure in top floor rooms) are especially vulnerable. EAI works with clients to identify these blind spots through system mapping and routine visual inspections.

Case Study: Legionella Found in Domestic Showers and Upper Floor Plumbing

EAI supports numerous healthcare facilities in identifying hidden risks in underused or low-flow plumbing fixtures. One of the most underestimated sources? Infrequently used showers—especially those located in patient rooms, rehabilitation units, and staff locker areas. When paired with aging hot water tanks, inconsistent recirculation, or poorly balanced cold water lines, these fixtures can become sites of elevated Legionella activity.

In one instance, a hospital’s top floor patient wing equipped with new systems but suffering from lower pressure and irregular water flow tested positive for Legionella in multiple domestic showers. Investigators found that cold water stagnation in underused outlets, combined with slow temperature rise from hot water tanks, created ideal conditions for bacteria to thrive.

A study published by MDPI evaluated 68 domestic showers using quantitative PCR (qPCR) methods and found:

• 74.6% of samples were positive for Legionella spp.
• 64.2% contained Legionella pneumophila, the strain responsible for most Legionnaires’ disease cases
• Concentrations ranged from 2.5 to 110,000 copies/mL in contaminated water samples

These findings align with what EAI field teams routinely observe during healthcare water system site audits. Showers and outlets located on upper floors or at the ends of distribution systems often have delayed water delivery, reduced disinfectant levels, and become harder to control without targeted flushing protocols.

To control Legionella growth in such areas, EAI works with healthcare clients to assess water supply flow rates, balance hot and cold water pressure, and implement scheduled use or automated flushing in distribution system zones with reduced occupancy.

High-Risk Patient Populations in Healthcare Facilities

Not all patients face the same risk from Legionella exposure. In healthcare environments, certain individuals are significantly more vulnerable to opportunistic pathogens like Legionella pneumophila, and without appropriate control measures, even minor system lapses can result in severe outcomes.

Those most at risk include:

• Adults over 60 years old
• Patients with chronic respiratory conditions
• Individuals undergoing chemotherapy or immunosuppressive therapy
• People with diabetes, kidney disease, or compromised immune systems
• Patients with neurological issues or swallowing difficulties, which increase the risk of aspirating contaminated water

For these populations, Legionella infections can escalate rapidly, often requiring hospitalization for pneumonia or, in worst cases, resulting in death. Healthcare facilities must treat waterborne pathogens as clinical hazards and ensure their systems are engineered not just for comfort, but for safety.

The Rise of On-Site Long-Term Care

As the global population ages and demand for in-home and long-term care rises, more vulnerable individuals are relying on domestic water systems not originally designed to manage opportunistic pathogens like Legionella. These new systems are often installed quickly during home retrofits or care expansions, and may lack critical components like thermostatic mixing valves, flushing protocols, or water management oversight.

In many cases, private homes or assisted living units experience:

• Inadequate monitoring of domestic hot water temperatures, leading to conditions that support bacterial growth.
• Irregular water flow due to sporadic use of showers or faucets from drinking water sources, which allows stagnation and biofilm formation.
• Neglected or unserviced water filters, which may actually harbor microbial contaminants if not properly maintained.

As cited by World Health Organization, by 2025, over 25% of the global population is projected to be over 60 years old. Many of these individuals will be relying on domestic water systems for daily hygiene, wound care, and medical device cleaning, raising the stakes for public health safety.

EAI Water frequently partners with healthcare networks, senior living communities, and in-home care providers to assess, retrofit, and maintain domestic plumbing systems. Our field teams conduct risk assessments, recommend temperature and pressure adjustments, and develop simplified water safety routines that can be followed by caregivers or facility staff.

Legal Exposure When Legionella Control Measures Fail

In healthcare, the consequences of a Legionella outbreak extend far beyond infection control—they can often lead to legal liability, operational disruption, and reputational harm. Lawsuits stemming from Legionnaires’ disease cases within water distribution systems frequently cite poor water supply system maintenance, lack of a functional water management program, or failure to implement basic control measures.

Here are several high-profile examples that underscore the importance of being equipped for waterborne pathogen prevention:

• Wingate Inn Hot Tub Contamination (2010):
  Though not a healthcare case, this $4.5M settlement remains a benchmark in legal accountability. Investigators found lapses in disinfection and temperature control in a whirlpool spa, setting a precedent for negligence tied to water system oversight.
  Takeaway for healthcare: If your facility uses therapy tubs, rehabilitation showers, or hydrotherapy equipment, ensure they are equipped with documented flushing routines and temperature logs.
• Flint Water Crisis (2014–2019):
  Improper treatment after a municipal water source switch led to widespread Legionella outbreaks and lead contamination. Though centered in municipal infrastructure, this case reinforced how unmonitored operations and failure to maintain disinfectant residuals can have fatal consequences.
  Takeaway for healthcare: Transparent operations and control measures—including corrosion protection and residual disinfectant tracking—are essential, especially when relying on external water supply systems.
• Bronx Cooling Tower Outbreak (2015):
  A major Legionella outbreak in New York City resulted in over 100 illnesses and 16 deaths. The facility failed to comply with Local Law 77, which mandates Legionella testing and maintenance for cooling towers.

Regulatory Expectations in Domestic and Institutional Settings

From national standards to local mandates, the pressure is growing for healthcare facilities to implement robust water management programs, conduct regular visual inspections, and equip their water supply systems with monitoring and disinfection safeguards.

Here’s how the most cited guidelines shape control measures in healthcare environments:

ASHRAE Standard 188

ASHRAE 188 provides the foundational framework for developing a water management plan in buildings with complex distribution systems. For hospitals, long-term care homes, and outpatient centers, it requires:

• Risk assessments for all distribution systems, including hot and cold water loops, showers, tanks, and therapeutic devices
• Ongoing microbial monitoring, corrective measures, and documentation
• A multidisciplinary water safety team to oversee operations and system updates

Though voluntary at the national level, ASHRAE 188 is increasingly referenced in litigation and state laws, making it an essential baseline for compliance.

OSHA Guidelines

OSHA places specific emphasis on preventing Legionella exposure in high-risk workplaces, particularly in healthcare facility water supplies. Key recommendations include:

• Maintaining hot water outside Legionella’s growth range (77–113°F)
• Flushing low-use outlets and documenting visual inspections
• Training engineering and maintenance staff on how to recognize and respond to contamination risks

EPA Recommendations

While the EPA focuses on public water supply systems, its guidance reinforces the importance of controlling microbial growth inside buildings through:

• Limiting biofilm formation in distribution systems
• Maintaining disinfectant residuals
• Avoiding practices that compromise system integrity (e.g., backflow, cross-connections)

Facilities are encouraged to coordinate with local municipal suppliers to ensure their water supply system supports facility-level prevention strategies.

State and Local Laws

States like New York, New Jersey, and Illinois have introduced specific Legionella legislation. For example:

• NYC Local Law 77 mandates testing and disinfection for all cooling towers
• New Jersey requires public and healthcare facilities to submit water safety plans and maintain disinfectant residuals
• Many states require reporting Legionnaires’ disease cases within 24 hours

Regardless of whether these rules apply locally, EAI advises healthcare clients to treat them as best-practice benchmarks. Because in the healthcare setting, falling short of expectations is never just a regulatory issue; it’s a patient safety risk.

Prevention Strategies for Domestic Water Systems in Healthcare

Proactive water management remains the single most effective strategy to prevent Legionella growth in healthcare facilities. At EAI, we help clients move beyond reactive testing and toward fully integrated control measures that safeguard patients and ensure compliance.

Here are the most critical prevention strategies for domestic hot and cold water systems:

1. Maintain Hot Water at Safe Temperatures

Keep domestic water (hot) circulating at 130°F (54°C) and use thermostatic mixing valves at point-of-use fixtures to prevent scalding. This prevents water from dropping into the temperature range where Legionella thrives, particularly in extended distribution systems.

2. Flush Underused Outlets Routinely

Outlets not used at least weekly (such as showers in unoccupied rooms or sinks in low-traffic areas) should be flushed per your water management plan. Flushing of drinking water helps maintain disinfectant levels, reduce stagnation, and improve overall water flow.

3. Inspect and Replace Filters on Schedule

Point-of-use and central filtration systems should meet microbial reduction standards (e.g., NSF/ANSI 53 or 58) and follow a documented maintenance schedule. Visual inspections and filter replacement logs are essential for confirming performance and preventing hidden sources of contamination.

4. Test High-Risk Zones Regularly

Conduct microbial testing after disinfection events, plumbing changes, or in response to complaints. Focus on known problem areas such as long pipe runs, cold water dead legs, or patient wings with intermittent use. EAI provides onsite sampling and third-party lab analysis customized for healthcare environments.

5. Document Every Control Measure

Maintain logs of temperature readings, disinfection events, visual inspections, and corrective actions. Your water management program should remain a living document, updated in response to test results and system changes.

EAI in Legionella Control for Healthcare

At EAI, we bring over 30 years of experience helping healthcare facilities identify, manage, and control Legionella risks in their potable water supply systems. Our approach goes beyond basic compliance—we engineer science-backed control measures that safeguard patients, satisfy regulators, and empower your operations team.

Here’s how we support your water safety goals:

Custom Water Safety Plans (WMPs)

We design ASHRAE 188-aligned plans tailored to your building layout, patient population, and regulatory obligations – integrating testing schedules, control limits, flushing protocols, and emergency response workflows.

Advanced Microbial Testing

EAI offers both routine and event-driven testing, including Legionella pneumophila, biofilm indicators, and residual disinfectant levels. We work with trusted labs to deliver reliable results, trend analysis, and actionable reporting.

Disinfection and Emergency Response

From system-wide chlorination to targeted online disinfection, our experts provide turnkey solutions when contamination is detected or when proactive maintenance is due. We also support emergency disinfection planning.

Operator Training and Support

We train your engineering, nursing, and environmental services teams on how to monitor, report, and respond to water quality risks. Education is one of the most effective tools for reducing preventable exposure events.

Healthcare Adaptations

EAI supports a wide range of healthcare environments from hospitals and outpatient centers to long-term care homes and rehabilitation facilities. We adapt our commercial-grade water safety strategies to meet the specific needs of these sensitive settings, where infection prevention and regulatory compliance are non-negotiable. Our work helps healthcare teams maintain clean drinking water, reduce exposure risks, and safeguard patient health.

Take Control of Your Water System Risk

Legionella control isn’t just about responding to a positive test, it’s about building a system that prevents one. Whether you manage a critical access hospital, an outpatient clinic, or a long-term care facility, EAI gives you the tools and confidence to manage your water systems with precision.

Let’s build a safer system together. Contact EAI to start your water risk assessment today.