A building’s water system is its lifeblood – circulating through pipes, cooling towers and storage tanks every day. But hidden within that system can be an invisible threat: Legionella bacteria. When water stagnates, sits at lukewarm temperatures, and/or there is biofilm in the system, Legionella and other bacteria can multiply. Once aerosolized through showers, humidifiers, hot tubs, fountains, or HVAC system components, they can cause Legionnaires’ disease – a serious and sometimes fatal respiratory infection.
For building owners and facility managers, controlling Legionella bacteria and biofilm isn’t just about ticking a compliance box. It’s about protecting people, maintaining trust and ensuring operational resilience.
Understanding Legionella in Building Water Systems
Legionella bacteria occur naturally in freshwater but can amplify in engineered water systems found in commercial, healthcare, institutional and residential buildings. Common high-risk systems include:
- Cooling towers and evaporative condensers.
- Domestic hot and cold-water systems.
- Decorative fountains and spas.
- Humidifiers and misting systems.
- Structures with little to no occupancy and other unused pipe sections.
The bacteria actively grow between 77°F and 113°F (25°C–45°C), particularly in stagnant water with biofilm in the systems. Aging infrastructure, complex plumbing and low-flow systems often installed to save energy can unintentionally create ideal growth conditions, turning routine water systems into potential health risks.
Why Legionella Risk Management Is a Growing Priority
Cases of Legionnaires’ disease have increased globally over the past decade. According to the CDC, thousands of U.S. cases occur annually, of which many go undiagnosed or misattributed. Similar patterns are seen across Europe and Asia.
Key factors driving this rise include:
- Aging building infrastructure and deferred maintenance.
- Rising ambient temperatures due to climate change.
- Periods of low occupancy or building downtime.
- Inconsistent water temperature regulation in modern low-flow plumbing.
For facility leaders, these realities highlight one message: proactive Legionella management is critical for health, compliance and operational continuity.
Regulatory Landscape: Staying Ahead of Compliance Requirements
Legionella risk management is now a regulatory expectation across sectors from healthcare to hospitality to education.
Key frameworks include:
- ASHRAE Standard 188: Defines water management program requirements to reduce Legionellosis risk in buildings.
- CDC Water Management Toolkit: Provides step-by-step guidance for developing a Water Management Plan (WMP).
- CMS (Centers for Medicare & Medicaid Services): Requires healthcare facilities to actively control Legionella risk.
- HSE L8 (UK) and ISO 11731: Establish global standards for monitoring and testing.
Legionnaires disease outbreaks can result in public health incidents, reputational damage and costly remediation. Proper documentation, testing and ongoing validation are essential for demonstrating due diligence.
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Best Practices for Legionella Risk Management in Buildings
Effective Legionella prevention relies on a layered, evidence-based strategy that integrates engineering, maintenance and monitoring.
- Temperature Control
Maintain hot water throughout the water systems above 120°F (49°C) and cold water below 77°F (25°C) to inhibit bacterial growth. Higher temperatures should be maintained in some system components, such as hot water holding tanks at 140F, if possible. - System Design Optimization
Eliminate “dead legs,” low-use outlets and complex pipe loops where stagnant water can accumulate. - Routine Flushing
Schedule systematic flushing to maintain water circulation and prevent stagnation. - Disinfection and Treatment
Apply targeted treatments, including chlorine dioxide, copper-silver ionization, ultraviolet (UV) disinfection, or thermal eradication based on building type and system design. - Maintenance
Promptly implement plumbing system repairs and ensure routine draining and disinfection of cooling towers to keep your systems in optimal operating condition while minimizing harbourage potential from conditions such as scale, silt, and biofilm accumulation. - Continuous Monitoring and Data Analytics
Use smart sensors and IoT monitoring to track temperature, chlorine levels and flow conditions in real time for early detection.
Together, these measures form the backbone of a comprehensive Water Management Plan (WMP) – the gold standard for Legionella control and regulatory compliance.
TRC’s Approach: Comprehensive, Data-Driven Legionella Management
At TRC, we combine engineering expertise, industrial hygiene and environmental science to help clients stay ahead of Legionella risks.
Our Certified Industrial Hygienists (CIHs) and Environmental Health & Safety (EHS) practitioners design customized Water Quality Management Plans (WQMPs) tailored to each facility’s operational profile and regulatory needs.
Our services include:
- Comprehensive Legionella testing and risk assessments.
- Development and implementation of custom WQMPs.
- System design reviews and remediation planning.
- Emergency response and outbreak mitigation support.
- Collaboration with CDC ELITE, NYS ELAP and A2LA-accredited laboratories for accurate, defensible testing results.
From commercial high-rises and healthcare facilities to campuses and government buildings, from potable water distribution to cooling tower basins, decorative fountains, and everything in between, TRC’s integrated approach ensures your water systems are safe, compliant and built for the future.
Building Safer, Healthier Spaces Through Collaboration
Legionella prevention is more than compliance, it’s a shared commitment to health, sustainability and trust. Effective management requires collaboration among facility engineers, EHS teams, and public health professionals to build a strong water safety culture. With TRC as your partner, you can go beyond checklists to create resilient, future-ready buildings that lead in safety, sustainability and operational confidence.
