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How Do You Test for Legionella in Water?

Did you know that our water pipes contain a myriad of good bacteria that help improve the quality of our drinking water? It may be gross to think about, but the normal bacteria we drink in our water are harmless and healthy for us! However, on some occasions, bad bacteria can make their way into our drinking water. One of these bad bacteria is Legionella.
Most people have never heard of Legionella and don’t know the risks this dangerous bacteria presents. Keep reading to learn more about Legionella and how to prevent it from affecting your water system.

What Is Legionella?

Legionella is a dangerous bacteria that thrives and multiplies in water where temperatures are between 68 and 113 degrees Fahrenheit. A person can be infected by Legionella bacteria by breathing in small water droplets containing the bacteria. When a person is exposed to Legionella bacteria, they are at high risk of contracting Legionnaires disease, a severe form of pneumonia (inflammation of the lungs).
Legionella Bacteria can also make people sick with a less serious illness called Pontiac Fever, which has mild flu-like symptoms. Pontiac Fever usually clears up on its own and doesn’t require any additional treatment. However, Legionnaire’s disease will not resolve on its own and left untreated, can be fatal.

Legionella in Water Systems
Legionella is found naturally in freshwater areas like lakes, rivers, and streams. Legionella is not a concern in the wild but becomes a major problem when the bacteria grows and spreads to man-made water systems such as:

  • Water faucets
  • Showerheads
  • Hot tubs
  • Hot water tanks
  • Water heaters
  • Cooling towers
  • Plumbing systems 


Various conditions can cause Legionella to find its way into man-made water systems. One way is when a water disinfection system fails; if the water stops flowing, the disinfectant levels are not maintained, or the plumbing becomes stagnant, Legionella can take over that water system.
Another condition that allows for Legionella to survive and multiply in water systems is when the water temperatures are not hot or cold enough to prevent growth. Legionella lives and spreads in water temperature between 68 and 113 degrees Fahrenheit. Water temp should be maintained either below 65 degrees or above 122 degrees Fahrenheit to prevent harm.
Legionella does not die off when the water temperature is below 68 degrees, but the bacteria become inactive/dormant and does not multiply.

How to Test for Legionella

There are a few different ways to test for Legionella, and each method has different degrees of effectiveness. There are various detection methods and sampling methods. The two main detection methods for Legionella are:
Culture Method, PCR Method, DFA Method.

The Culture Method involves confinement of the bacterial filtrate on an agar petri dish, then the serum is identified using biochemicals. Results come back as either ‘Detected with Legionella’ or ‘Not Detected.’ One downside of the culture method is that it takes 10 days to complete, during which more occupants could become exposed to the Legionella bacteria in the water and get sick. 

The upside of the PCR (Polymerase Chain Reaction) method is that it only takes a few hours to complete and is useful for screening drinking water samples. However, the downside is that it does not work well with water samples that have been exposed to dirt or debris because the debris causes a background that masks the presence of Legionella.

The DFA (direct fluorescent antibody) Method was developed by the CDC in 1978 and is considered the best method to test for Legionella in both drinking and environmental water samples.  

Legionella During Covid

When Covid-19 turned the entire world upside-down at the beginning of 2020, businesses and companies were forced to shut down operations and lock up their buildings. Places of business stayed closed for many months until they were given the “OK” to start operations back up again. While these businesses were closed, their water systems were offline with little to no maintenance being done.
The water sat in these building pipes, becoming stagnant and creating perfect conditions for Legionella to move in. After the summer of 2020, businesses were allowed to re-open and begin operations; this created a huge risk of increased Legionnaire’s cases. If the water systems are not properly brought back online, sampled and tested for bacteria, or treated/sanitized, there could be an outbreak of Legionella-related illnesses.
Both Legionnaire’s disease and Covid-19 affect the lungs and respiratory system. Because they present similar symptoms, health care workers are more inclined to test pneumonia cases for Covid-19, not realizing Legionnaire’s disease may be the culprit. The earlier and quicker a proper diagnosis is made, the sooner treatment can begin for Legionnaire’s disease, preventing the illness from worsening and even death.

Legionella Prevention

Many steps and methods can be taken to help prevent and minimize Legionella bacteria from getting into your water supplies in the future. These steps will help keep your water systems clean and safe.

  1.  Develop a water management program to regularly test your water system. There are toolkits that provide step-by-step instructions on how to set up water management programs.

  2.  Make sure your water heater is maintained and working properly. Ensure that the water temperature is correctly set. Water should be kept at temperatures that Legionella cannot survive or multiply in.

  3. Flush your water system when necessary. Flushing the system will get rid of any stagnant or bacteria-infected water.
  4.  Make sure cooling towers are clean and maintained.
    5. Conduct regular Legionella testing. Incorporating routine environmental sampling for Legionella will help catch any signs of the bacteria early enough to stop it before it spreads.
  5.  Conduct regular Legionella testing. Incorporating routine environmental sampling for Legionella will help catch any signs of the bacteria early enough to stop it before it spreads.

Water System Tips and Trends

Now that you know all about the dangers of Legionella, the conditions it grows in, and how to prevent this bacteria from infecting your waters, you’ll be able to protect your occupants and yourself from bacteria-caused illnesses.
To learn more about proper water system management and increase your knowledge of bacteria prevention, head on over to our Legionella Resource Center page to stay up-to-date and informed on water system maintenance.


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