Points of risks for Legionella outbreaks

Points of risk
Learn to identify locations and potential causes of Legionella risks

Outbreaks of Legionella bacteria, which can cause Legionnaires’ disease, are a particular concern at healthcare locations such as hospitals, nursing homes, and long-term care facilities. The potential for a widespread outbreak is also a challenge for buildings in the hospitality industry, such as hotels, motels, and resorts.

Successful mitigation of Legionella requires identifying where bacteria may exist in your water system, and understanding the underlying conditions that may allow outbreaks to occur. Learn how to address all the risks ... 1) Points of source, 2) Points of use, and 3) Points of condition by exploring the example facilities below.

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Points of Source

Icon showing Legionella Point of Source

These risks are located within the equipment and plumbing that treat, conduct, and distribute water throughout your facility. Evaluate how your system takes incoming water from the municipality and trace the flow from your mechanical room into and out of such equipment as heaters, chillers, and cisterns.

Incoming Water

Water is usually provided from a local municipality and typically has been treated with chemicals at the plant before traveling to a building. Organizations do not know the levels of chlorine or other chemicals at the original point of treatment, nor how much has dissipated during travel.

Water Heaters

Circulation and temperature in hot water tanks can vary. This can create an environment where scale and sediment can accumulate, creating a perfect environment for legionella growth.

Points of Use

Icon showing Legionella Point of Use

These risks are located wherever people interact with the water distributed throughout your facility. Obvious places to look are faucets, showerheads, ice machines, drinking fountains, and decorative fountains. But you will also want to look at any equipment that uses water, such as hot tubs and hydrotherapy spas.

Faucets and Showerheads

Public bathrooms, private rooms, and kitchens can be the source of numerous risks. As water travels from the mechanical room throughout the building bacteria grows back into the system if the mechanical valve set point is below 126° F on the return line. If there are dead legs and/or the water sits within the piping at the faucet or showerhead and becomes stagnant causing new growth of Legionella.

Pools, Therapy Pools, Hot tubs

Steam and mist generated from a heated pool or hot tub can be aspirated into the lungs, putting guests and patients at risk of exposure to Legionella bacteria.

Ice Machines

In 2013 three Legionnaires’ cases were documented as caused by patients choking on ice chips. According to Janet Stout, Special Pathogens Laboratory, “Research confirms ice machines as a potential source of exposure for some cases of Legionnaires' disease. Our 1985 study, showed that while ice dispensers are supplied with cold water, the condenser/compressor can heat the piping inside the machine and warm the cold water enough to support bacterial growth. The charcoal filter on the cold water line removes chlorine and can become colonized. That water is ultimately dispensed or made into ice. Most bacteria do not multiply in ice, but they can survive at these low temperatures.”

Ornamental Water Features

Water features including decorative fountains have been associated with Legionnaires’ disease outbreaks. Most reported outbreaks have been associated with indoor ornamental water features but there is at least one case documented related to an outdoor water feature, according to “Guidelines for Control of Legionella in Ornamental Water Features”, Tim Keane of Legionella Risk Management, Inc., in a report commissioned by the South Dakota Department of Health.

Drinking Fountains

Most bacteria contamination comes from the rims and handles of the fountain but Legionella is still a risk. According to a recent CDC report on waterborne diseases in drinking water, public health officials from 14 states reported 32 outbreaks linked to drinking water between 2011 and 2012. These outbreaks resulted in hundreds of illnesses and 14 deaths. Most of the cases were associated with Legionnaire’s disease, with the remaining cases caused by Norovirus, E. coli, Shigella, Giardia, or other pathogens.

Points of Condition

Icon showing Legionella Point of Use

These risks are often overlooked… the underlying conditions that can make your water system more vulnerable to Legionella. These conditions can exist in locations throughout your facility including points of source and points of use and are all precursors to a potential Legionella outbreak and or recurrence.

Dead Legs in Piping

Dead legs are places within the piping system where there is little or no water movement most of the time. Water collects in these spaces and bacteria such as Legionella can quickly grow. Solutions such as heat, chlorine, and UV are typically ineffective at these remote locations, leaving your facility at risk. Often the locations of dead legs are unknown making it even more challenging. Dead legs can be the result of renovations throughout the years or poor overall system design. Eliminating dead legs is very hard so in order to combat them most in the industry propose some kind of point-of-use solutions such as filters and heat.

Stagnation in Piping

Water can become stagnant in dead legs of faucets, showerheads, and other piping areas due to low circulation or low water flow. Stagnant water creates the perfect environment for scale and bacteria to grow causing a breeding ground for Legionella formation.


Heat as a Legionella control solution introduces the fear of scalding and compromising the safety of people in the building. ASHRAE 188 recommends 140° F as the baseline temperature to kill the bacteria within 30 minutes. On average, any water that is above 106° F can cause pain in humans while water that is 140° F can cause third degree burns in a matter of seconds.

Incoming Water from Municipality

Most water coming into your facility from a municipality will have chemicals already injected including chlorine. However, as an organization you cannot rely on these chemicals to protect against Legionella growth because you do not normally know the amount of chlorine or chemical in the water, municipalities commonly change chemical dosages throughout the year, and chemicals dissipate as they travel and time lapses.

Chemical Dissipation

As water travels from the municipality to your building, chlorine and other chemicals within it will have dissipated. Additional chemicals injected into your system will also begin to dissipate as the water travels through your piping, increasing the chance for Legionella to grow. A point-of-use solution needs to be added in addition to chemical injection.

Corrosion from Chemicals

Many solutions for Legionella growth can also create corrosion and damage to piping systems and equipment. Chlorine and other chemicals are culprits of corrosion. The damage, maintenance, and possibly the replacement of these should be considered when using chemicals as part of your water management plan.

Lack of Circulation through Piping

Constant circulation of water through the piping system is important to decrease the chance of scale forming. If there isn’t good circulation then dead legs or stagnant water can form creating an area of food for Legionella growth.

Low Water Flow

Many regulating bodies and organizations have adopted codes and practices implementing low flow faucets in an effort to conserve water and be environmentally friendly. While low flow mechanisms can reduce water usage, their use should be carefully considered in light of potential Legionella outbreaks. Low flow devices and practices limit the movement of water, which can create environments where scale develops and Legionella thrive.


Sediment is commonly found in a building’s water supply. This sediment can turn into food for Legionella and can also dilute the effectiveness of solutions you may have implemented to reduce Legionella growth. Sediment can cause shadows in the water and essentially block UV and copper ionization solutions from being able to kill Legionella or make it dormant. A sediment-reducing solution should be considered important for a water management plan.

Scale in Water Heaters

Scale serves as food for Legionella. In a hot water tank, heating elements can become coated with scale, reducing system efficiency and increasing the chance for bacteria such as Legionella to grow.