Water Safety Considerations: 3 Practical Steps to Reduce the Risk of Legionella and Waterborne Pathogens 

Written by Erich Knemeyer

Legionella is a serious concern for anyone managing building water systems. Found in warm, stagnant water, this bacteria causes Legionnaires’ disease—a potentially deadly form of pneumonia. For hospitals, schools, hotels, and other high-traffic facilities, Legionella prevention isn’t optional; it’s essential. While Legionella isn’t the only waterborne pathogen, it seems to get the most headlines.

Legionella bacteria, naturally occurring in freshwater, become hazardous when they multiply in warm, stagnant water systems (77°F-113°F), especially those with biofilm buildup. Transmission occurs when contaminated water droplets (aerosols) are inhaled, often from cooling towers, hot tubs, sinks, or showerheads. The dirt and scale that form within water systems provide nutrients for bacterial growth.   When the Legionella growth reaches a high enough level, the risk of contracting Legionella disease greatly increases.  Facilities such as hospitals and nursing homes, or individuals with depressed immune systems, are at the highest risk. 

These practical and proven steps and solutions have been shown to reduce the risks posed by Legionella and other waterborne pathogens.

1. Maintain Optimal Water Temperatures

Legionella thrives in warm water, especially temperatures between 77°F and 113°F (25°C and 45°C).  Generating hot water at or above 140°F is critical to kill the bacteria. Regularly monitoring and recording water temperature is critical, especially during off-peak usage and recovery periods.

The fix: Set, generate, monitor, alarm, and track hot water temperatures.

We use Armstrong International’s Digital-Flo® water heating technology with digital controls for fast, accurate hot water delivery. Constant low-pressure steam heats all the water entering the exchanger to temperatures well above Legionella bacteria’s living range, reducing the chances of bacterial growth. Digital-Flo solutions reduce microbial growth without using harsh chemicals.

2. Implement Effective Disinfection

One of the biggest challenges in Legionella prevention is biofilm—the slimy layer inside pipes and tanks where bacteria hide and multiply. Regular disinfection of water systems is essential to controlling Legionella effectively. This typically involves using approved disinfectants like chlorine or other biocides at appropriate concentrations, ensuring consistent levels throughout the system. However, traditional cleaning methods can’t always reach the biofilm. Consider supplementary disinfection methods to minimize the risk of bacterial growth in high-risk areas.

The fix: Clean the system and keep it clean. 

The Nanobubble Generator brings a new level of protection to water systems. Unlike traditional water treatment methods that rely on harsh chemicals or high heat, nanobubbles use the power of ultra-small oxygen bubbles to clean your system from the inside out. Negatively charged nanobubbles attract the impurities in the water that typically attach to heat exchangers and pipe walls.  They also act like scrubbing bubbles to slowly remove the typical buildup you see in domestic water pipes and exchangers.  This sustainable, easy-to-install, non-electric solution is environmentally friendly and enhances the lifespan of your equipment.  

3. Minimize Stagnant Water

Stagnant water is a breeding ground and makes for an ideal environment for Legionella to multiply. Any part of a water system where water sits unused for extended periods such as unused pipes, infrequently used fixtures, poorly circulated storage tanks, long plumbing runs, and low-demand areas can cause the bacteria to grow and thrive. Flushing infrequently used taps and showerheads regularly can significantly reduce this risk.

The fix: Use a master mixing valve that does not use aquastats.

The Brain® Digital Recirculation Valve from Armstrong International requires a minimum constant recirculation flow (no aquastats tied to pumps) and reduces the risk of stagnant water in the main loop. The valve’s three integral thermistors check hot inlet and cold/return temperatures every 4 seconds and correct temperature fluctuations in real-time. It supplies precise, consistent hot water, eliminating temperature swings that create ideal conditions for Legionella.  In addition to superior temperature control, The Brain can alarm when water temperatures are outside of design conditions and can be part of a tracking and trending system that infection control management may need.

By prioritizing water safety and implementing these practical steps, you can significantly reduce the risk of Legionella and other waterborne pathogens in your facility. Don’t wait for a crisis to act—start today and ensure a safer environment for everyone. Connect with Merlo Energy to learn how we can help with thermal high-temperature sanitation and domestic hot water temperature setting, monitoring, alarming, and trending. 

Resources to help with Water Safety program:  

VA Directive 1061(D)

ASHRAE Standard 188-2021