Reducing the Growth of Legionella Bacteria in Distributed Water Systems

Nearly 50 years ago, the first identified cases of Legionnaires’ disease were confirmed during a convention of the American Legion in Philadelphia, Pennsylvania. Since 1976, the study of how Legionella bacteria live, interact, and multiply in building water distribution systems continues to provide valuable information. Despite an increase in the understanding of the bacteria, the Centers for Disease Control (CDC) indicates Legionnaires’ disease has been on a steady rise since 2000. Is this increase due to better monitoring for the disease, an aging population, or other factors that influence the growth of the bacteria? Aside from the clinical aspects, there are many physical and mechanical variables to consider: water flow, water temperature, building pipe age, and the quality of water supplied to the building. These and many other variables all play a part.

One of the key elements in reducing Legionella bacteria in building water systems is replacing the water in the pipes often enough to prevent stagnant water conditions. Flushing the water and replacing it with fresh, disinfected water from the municipal supply should be incorporated into the building water management plan. Bacteria – especially Legionella — thrive in low-flow water conditions where biofilm can develop. However, water scarcity and conservation requirements may run counter to this frequent flushing recommendation, and many hospitals have incorporated flow restriction devices on faucets and showers with the good intention of saving water. Unfortunately, when this occurs, a condition of poor water exchange and stagnation develops — along with it, an environment conducive for Legionella growth.

Use the Internal Experts

Many hospitals maintain an internal infection control program, managed by doctors and nurses trained in hospital-acquired disease management. Additionally, other members of the infection control group may include Facilities Management and Environmental Services. The role of Facilities Management and Environmental Services cannot be understated in reducing the risks associated with Legionella bacteria.

Facilities Management will always be involved in building domestic water piping, water use restrictions, hot water temperature control, and any pipe isolations, when necessary. If water use needs to be restricted, accessed, or expanded, Facilities Management is responsible. Environmental Services are responsible for the upkeep and cleaning of patient rooms and bathrooms. These two management groups, as explained below, can use several techniques and actions to reduce Legionella growth in hospital water distribution systems.

The Environmental Services group is often overlooked in a water safety program as holding a significant role in waterborne bacteria reduction, but this group can be effective in the battle against Legionella. How so? Simply stated: they are in the patient rooms on a regular basis, specifically, in between patient use and occupancy. During these cleaning and upkeep visits, they can flush water (initial high volume burst then reduced to low volume flow) in the shower and sinks for the period they are working in the room. This easily implemented flush procedure will have the impact of moving water that may be sitting stagnant for days at a time, to water that is direct from the main, and should have a higher disinfectant residual.

When it comes to bacteria reduction in distributed water systems, there are three main areas of concern: water flow (or stagnation), temperature, and disinfectant residual. When water is allowed to stay in the building pipes for days, stagnation will affect all three. Domestic cold water will increase in temperature to the ambient environment temperature of 68-77°F (20-25°C), chlorine disinfectants will be reacted or reduced, and biofilm develops. Replacing old water with fresh water may seem wasteful, but it could be an effective technique for keeping Legionella at zero or a very low concentration. Some hospitals now require Environmental Services to incorporate this flushing procedure for sinks and showers (hot and cold) and include this as policy into their Environment of Care Management Program.

Facilities Management, because of their building piping responsibilities, can also have an impact on Legionella bacteria reduction. Here are some examples:

  • Coordinate a building water quality profile by collecting disinfectant residuals and temperature data from a representative sampling across the hospital. The sampling regimen should be outlined in the Water Management Program. Having building water profiles will identify potential bacteria growth areas and indicate if there is adequate water flow and disinfectant residuals.
  • Identify and eliminate (if possible) deadlegs in the hot and cold distribution system. Deadlegs equal stagnant water.
  • Maintain domestic hot water at the highest temperature allowed by state regulations or codes. Legionella growth is optimal in the temperature range of 77-113°F (25-45°C).
  • If the hospital uses hot water tanks for storage, bottom blow each tank daily to prevent temperature stratification. Blowing down the tanks also creates turbulent flow, removes collected deposits, and disturbs biofilm growth. Domestic hot water storage systems should be designed, so the water does not remain in the tank for more than 24 hours.
  • Domestic hot water circulation pumps should operate continuously; they should be excluded from energy conservation measures. Circulation pump operation should be checked routinely.
  • If disinfectant residuals cannot be maintained in the hot water distribution system, consider bleeding a small flow to drain off the hot water return line. This will ensure fresh disinfected water is always flowing into the hot water lines. Hot water use declines at night, so for several hours each night, the hot water distribution lines that are not in circulation become stagnant and areas for potential biofilm growth.
  • If the hospital has isolated a building wing for renovations, Facilities Management should coordinate with infection control personnel and develop a protocol for periodically flushing the water in the isolated distribution lines. Often, during a renovation, the water distribution system is left to sit without any exchange of water. Corrosion byproducts form, biofilm develops, and bacteria can amplify to very high levels. After renovations, if the piping is not disinfected or just opened up for use, patients and staff are at an increased risk for waterborne pathogens. Include building renovation water flush procedures in the Water Management Plan.
  • Implement a regular preventative maintenance program to replace shower heads in patient rooms. The cost of new plastic shower heads is often under $50, and when factoring in the time and labor needed to remove, clean, and replace the old ones, it may be a more efficient solution.
  • Consider removing “smart” water valves. These electric eye actuated valves contain many mechanical parts, and as a consequence, there is an increased surface area for biofilm growth. These valves are good for water conservation but potentially increase bacteria.
  • Bypass or redundant water supply lines should be valved open to ensure water flow. Many bigger buildings have more than one water supply line. If the line is consistently valved off, this water becomes stagnant, allowing bacteria to proliferate. A procedure for flushing the alternate supply lines should be included in the Water Management Plan.


Hospitals that are Joint Commission accredited now have the additional requirement of maintaining a Water Management Plan that includes methods and documentation for reducing the growth and exposure potential to Legionella bacteria. These water management plans center around reducing the growth of Legionella in distributed water systems, which is crucial for preventing Legionnaires’ disease. The key elements in reducing the bacteria include replacing the water in the pipes often enough to prevent stagnant water conditions and incorporating frequent flushing and fresh disinfected water into building water management plans. Additionally, utilizing the expertise of internal infection control programs, including Facilities Management and Environmental Services, can be effective in reducing the risks associated with Legionella bacteria. Techniques — such as flushing water in patient rooms, maintaining water flow and disinfectant residuals, and identifying and eliminating deadlegs in the hot and cold distribution system — can all play a role in reducing the growth of Legionella in distributed water systems.

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