Legionella—Stagnant Water, Beware!

Still water is great for a lot of different things. A calm lake is much more fun for a day of fishing, swimming or boating. However, stagnant water in the pipes of a domestic hot water system can lead to trouble. Warm, still water that has been hanging out in pipes for months can be the ideal place for Legionella bacteria to grow. How do we reopen commercial buildings safely while minimizing Legionella bacteria growth in plumbing lines?

Legionella bacteria exists in fresh water everywhere. Each drop of water that comes into a plumbing system from a municipality or well may contain colony-forming units of Legionella bacteria. In cold water the bacteria stay dormant so it’s benign. Unfortunately, when heated to a range between 68ºF and 122ºF, the bacteria start to multiply. Like COVID-19, Legionella bacteria can enter your body through your lungs. Inhaled droplets of water containing the bacteria can make you sick with pneumonia-like symptoms, roughly ten days after exposure.

According to the Center for Disease Control and Prevention, “Health departments reported nearly 10,000 cases of Legionnaires’ disease in the United States in 2018. However, because Legionnaires’ disease is likely underdiagnosed, this number may underestimate the true incidence. A recent study estimated that the true number of Legionnaires’ disease cases may be 1.8–2.7 times higher than what is reported.”
In 2021, we need to pay extra attention to the topic of Legionella. Many hotels, schools, offices and daycare centers have been operating at low occupancy, meaning the water isn’t flushed through to fixtures as often as during normal occupancy. The technical term for this delayed usage topic is “water age.” A drop of water that spends a month making its way from the meter to the showerhead has a high water age. Disinfectants from the municipality, like chlorine, may have long lost their effectiveness in controlling bacteria.

COVID-19 potentially bumped up the water age in many buildings, leaving them at higher risk for Legionella growth.

If you find yourself standing in a mechanical room deciding how to best combat Legionella bacteria growth, you have a couple choices. Chemical disinfection is sometimes utilized in emergency situations to kill bacteria. However, for an ongoing plan of attack, building occupants may not want to fill their water bottles up with something that smells like pool water. Additionally, if you start changing the chemistry of the potable water in a commercial building, you become your own mini-water municipality of sorts and now answer to the EPA. Know that you could bring additional government oversight into a project by assuming chemicals are being added to the potable water properly.

Thermal disinfection is a non-chemical way to take Legionella bacteria out of the growth temperature range and even kill the colony forming units in the lines you recirculate. You aren’t altering the water chemistry to kill the bacteria with this approach. You leave nothing new in the water when using thermal disinfection.

Imagine if your oven safely locked and cleaned itself once a week, while you are sleeping. No more having to check to see if the side dish from the Sunday BBQ spilled over and made a mess at the bottom of the oven. In a plumbing system, with the combination of an electronic point of distribution mixing valve, thermal balancing valves in the system branches and point of use mixing valves for scald protection you are essentially doing the same thing. In the Caleffi family, we use the LEGIOMIX® electronic mixing valve, ThermoSetter™ thermostatic balancing valves, and our fleet of point of use mixing valves. At a customizable time, you bump up the mixed temperature and circulate it through the lines at a temperature hot enough to kill the Legionella bacteria present. For a recirculated temperature of 140°F, you will need 32 minutes for the bacteria to die. For temperatures above 160°F, disinfection is instantaneous.

After your scheduled disinfection cycle wraps up, the building goes back into normal mixing operation. The LEGIOMIX has a minimal pressure drop, using a ball valve control element to control a wide mixed temperature range. It even has the ability to close the hot supply side off 100%, to prevent recirculation creep. Installing ASSE 1070, point-of-use mixing valves at the fixtures ensures protection from scalding at all times, even during a thermal disinfection cycle.

The playbook for Legionella management is simple. Heat and repeat. To reopen a building safely, post-quarantine, you need to continuously disinfect the recirculation lines, while maintaining scald protection.

Essentially, we are talking about plumbing system peace of mind for owners, engineers, plumbers and occupants in a year that has already had enough outbreak news. Sounds like a nice day at the lake.

Commissioning a new Caleffi flanged LEGIOMIX® at a hotel in Wisconsin. Dan Firkus, Caleffi Applications Engineer (left) with Service Technician from 1901, Inc. Photos and water temperature graphic courtesy Caleffi North America.

About the Author

Max Rohr is an education and training manager at Caleffi North America. He is a graduate of the University of Utah. He has worked in installation, sales, and marketing in the plumbing, hydronics, and solar industries since 1998. Contact: Max.rohr@caleffi.com

For more information regarding minimizing the risk of Legionella, visit SouthernPHC.com/Legionella.