Legionella is a type of bacteria that can grow in building water systems when conditions allow it to multiply. If people inhale tiny water droplets containing Legionella bacteria, they can develop Legionnaires disease, a serious form of pneumonia that poses a significant public health concern. Because many commercial and industrial facilities rely on complex water systems, preventing bacterial growth requires more than occasional cleaning. It takes consistent attention to system operation and maintenance.
Understanding how to prevent Legionella starts with knowing what encourages its growth and what practical steps help keep it under control. Throughout this guide, we’ll walk through the maintenance practices, temperature control strategies, water treatment methods, and routine inspections that reduce Legionella risks and help protect your facility, equipment, and building occupants.
What Makes Legionella Grow?
Legionella bacteria occur naturally in freshwater environments, but they become a concern when they enter man-made water systems. Unlike many other bacteria, Legionella thrives when conditions create an ideal environment for survival and multiplication. Warm water, especially when water temperatures stay between about 68°F and 122°F, encourages Legionella growth. Although temperature plays a major role, it is only one piece of the puzzle. Water quality, system design, and maintenance practices all influence how easily the bacteria can establish themselves.
Inside a plumbing system, scale, sediment, corrosion products, and biofilm provide surfaces where bacteria can attach and multiply. Biofilm is a thin layer of microorganisms that forms on pipe walls and water system components, making it harder for disinfectants to reach the bacteria. Areas with stagnant water, including unused pipe sections called dead legs, create even better conditions because water sits for long periods without enough movement or fresh disinfectant. These conditions support Legionella growth and allow bacteria to spread throughout the system if left unchecked.
Facilities should also pay close attention to stagnant or standing water caused by low water use, seasonal shutdowns, or oversized plumbing. Water that remains still for extended periods gradually loses disinfectant protection, increasing the opportunity for growth. The longer these conditions persist, the greater the risk that Legionella bacteria will multiply. Understanding these contributing factors is the first step toward learning how to prevent Legionella, because effective prevention always begins with eliminating the conditions that allow the bacteria to thrive.
Control Water Temperature First
Controlling temperature is one of the most effective ways to prevent Legionella growth. Research shows that Legionella multiplies most readily when water temperatures stay between 68°F and 122°F, with the fastest growth occurring in warm water. For that reason, most facilities store hot water in hot water tanks at 140°F (60°C) or higher, while circulating hot water at 120°F (49°C) or above. At the same time, cold water should remain below 77°F (25°C) whenever possible. Keeping hot and cold water within these recommended ranges makes it much harder for bacteria to survive and reproduce.
Maintaining these temperatures requires more than simply adjusting water heaters. Heat can gradually drop as water travels through long pipe runs, especially in large buildings where heat loss occurs before water reaches its destination. Regular monitoring helps confirm that the intended temperatures are maintained throughout the system, not just at the storage tank. Operators should also inspect recirculation systems, insulation, and equipment performance to ensure they continue operating within safe temperatures that discourage bacterial growth.
Facilities also need to balance Legionella control with user safety. Many buildings install thermostatic mixing valves to blend hot and cold water near fixtures, allowing the system to store water at temperatures that discourage bacteria while delivering water at a level that helps prevent scalding. Properly selected and maintained thermostatic mixing valves support both goals. Although some facilities use thermal shock treatments to temporarily raise temperatures, this approach alone is not a reliable long-term solution. Consistent temperature control, combined with routine maintenance and monitoring, remains the best strategy to minimize Legionella growth.
Prevent Stagnation Throughout the System
Moving water is healthier water. One of the simplest ways to reduce Legionella risk is to flush areas where water sits for too long. Low-use fixtures, little-used branches of the plumbing system, and sections with dead legs allow stagnant water to develop, creating favorable conditions for bacterial growth. We recommend flushing these areas at least once a week, especially after an extended period of low occupancy or shutdown. Keeping water moving helps bring in fresh disinfectant and reduces the time bacteria have to multiply.
Pay close attention to point of use fixtures such as sinks, shower heads, and faucets that people rarely use. Water can remain trapped in nearby water pipes, allowing disinfectant levels to decline over time. This is especially important in schools, hotels, healthcare facilities, vacation properties, or even a home water system that has been vacant for several weeks. As part of your routine maintenance program, make flushing these fixtures a regular task instead of waiting until someone reports a problem. For more practical maintenance tips, take a look at our guide to water system maintenance.
Regular flushing works best when it becomes part of a broader maintenance strategy. Operators should review system layouts, identify areas with poor circulation, and remove unnecessary pipe sections whenever possible. They should also verify that pumps, valves, and other equipment remain properly maintained under normal operating conditions so water continues to circulate throughout the water supply. These routine efforts may seem simple, but together they significantly reduce stagnation and help keep the entire system operating safely.
Water Treatment and Monitoring Strategies
Effective water treatment adds another layer of protection against Legionella. Temperature control and flushing remain essential, but facilities also need a reliable disinfection strategy to control bacterial growth throughout potable water systems. Maintaining an adequate disinfectant residual, often with chlorine or other approved disinfectants, helps limit bacteria as water moves through the system. Some facilities may also use calcium hypochlorite for shock disinfection when appropriate, although routine treatment should always follow regulatory requirements and system needs. The goal is to maintain clean water without compromising equipment performance or water quality.
A successful program also depends on consistent monitoring. Even the best treatment plan can become less effective if disinfectant levels, water quality, or system conditions change over time. Routine testing allows operators to verify that potable water remains protected and that treatment continues to control microbial activity before it becomes a larger issue. Regular sampling for disinfectant levels, chlorine, pH, and temperature provides valuable insight into system performance. Facilities with higher risk or complex systems should also consider routine Legionella monitoring. If you’re planning a monitoring program, our guide to Legionella testing explains what to expect and how testing supports a proactive maintenance strategy.
Every building has different operating conditions, so there is no single water management approach that works for every facility. Effective water management programs combine treatment, monitoring, inspections, and corrective actions into one coordinated plan. Always follow the manufacturer’s instructions for treatment equipment and the manufacturer’s recommendations for chemical products to achieve the best results. Regular reviews also help identify contaminated water, equipment issues, or changing conditions before they affect system performance. When facilities combine routine monitoring with a well-managed water treatment program, they gain better long-term control over Legionella while protecting both occupants and their water systems.
Higher-Risk Equipment and Buildings
Not every part of a facility presents the same level of risk. Equipment that creates small droplets or fine mists deserves extra attention because these droplets can be inhaled if Legionella contamination occurs. Some of the most likely sources include cooling towers, decorative fountains, hot tubs, and certain air conditioning systems that use water as part of their operation. When these systems are not cleaned, disinfected, and monitored regularly, they can release contaminated water droplets into the surrounding environment. That’s why routine inspection and maintenance are essential for reducing exposure.
Some buildings also require a higher level of vigilance. Hospitals, long-term care facilities, hotels, and large commercial buildings often have complex plumbing networks and many building occupants, making water management more challenging. People with weakened immune systems, older adults, and individuals with chronic lung disease or kidney failure face an increased risk of developing Legionnaires disease after exposure. Although healthy people exposed to the bacteria may not always become ill, no facility should assume the risk is low. Protecting water quality remains an important part of supporting public health.
The good news is that these risks can be managed with a proactive maintenance program. Regular cleaning, temperature control, water treatment, and inspections work together to reduce the conditions that allow Legionella to spread. Cooling towers, in particular, should receive specialized attention because they continuously circulate large volumes of water and can generate aerosols during normal operation. If you’d like to learn more about protecting these systems, read our guide to cooling tower water treatment. If anyone develops symptoms that may be related to Legionnaires disease after possible exposure, they should seek advice from a healthcare provider as soon as possible.
Creating a Long-Term Prevention Strategy
Learning how to prevent Legionella is really about building consistent habits instead of relying on one-time fixes. Flushing rarely used fixtures, maintaining safe water temperatures, monitoring disinfectant levels, and inspecting equipment all work together to reduce risk and limit bacterial growth. Strong water management practices also help facilities respond quickly when operating conditions change. Most importantly, protecting water systems requires ongoing attention because water quality can shift over time. A consistent approach helps maintain a safe water supply while protecting both equipment and building occupants.
Every facility has its own challenges, so prevention strategies should reflect the way the system is designed and operated. Regular reviews, routine testing, and proper maintenance make it easier to identify potential problems before they become costly or affect water quality. Looking to strengthen your Legionella prevention efforts? Talk to us. ProChem Inc. can help you evaluate your current program, recommend practical improvements, and develop a long-term water management strategy that keeps your systems operating safely, efficiently, and with confidence.
