How frequently you should test Legionella in a cooling tower will depend on various factors. These factors include:
Cooling towers transfer heated process water into chilled water, leaving many areas with ideal temperatures. Biocides being fed into the tower can significantly reduce the amount of Legionella present. Still, sometimes biofilms (a microorganism matrix that is resistant to chemical treatment) can form, and resist this. Additionally, cooling towers are seen as a significant risk due to the water aerosolizing when it evaporates. Making the bacteria airborne and able to contaminate people near the tower.
Legionella grows well in the specific range of 25°C to 45° or 77°F to 113°F. They colonize rapidly in these conditions and are known to be particularly robust. More frequent testing should be expected if the temperature in your cooling tower is kept high. Warmer months such as in the summer will be more at risk of forming Legionella, so it is important to keep that in mind when choosing when to take a test.
At-risk populations for Legionella include those over the age of 65, people who are immuno-compromised, and those who smoke (as Legionnaires’ disease is considered a lung infection/pneumonia). As such, hospitals, retirement homes, and other places with at-risk populations need to test more often as an outbreak could be particularly harmful. Hospitals often have additional requirements for regular testing which can vary on jurisdictions.
The location of your cooling tower should be of particular concern. Is it on a rooftop where people grill and use it as a common area? Is it close to ground level where people in the building have their windows open, or is there a sidewalk with pedestrians? And is the location near where at-risk populations would reasonably be?
Regular maintenance of your cooling tower will help control some of the risks of Legionella growing and the potential for outbreaks. Your cooling tower should have a water treatment program. Legionella bacteria are non-oxidizing, therefore non-oxidizing biocides should be fed at least. Scale, corrosion, and algae also make areas where Legionella can grow, so maintaining these issues will help with Legionella control too. Another factor to consider when maintaining the system is dead legs (areas of piping where water stays still) in or connected to your cooling tower piping. Stagnant water present in dead legs is extremely vulnerable to growing Legionella colonies. If you maintain your system regularly you can expect to need to test less often and vice versa.
Cleanliness plays a role in how often you will need to pull samples for Legionella testing. Semi-annual cleaning is generally recommended for cooling towers to not become too dirty, which can affect efficiency as well. If you clean your tower regularly you can expect to need to test less.
Recent laws have passed in 2024 requiring certain facilities to test for Legionella. States like Ohio and New Jersey, as well as cities such as New York City all have implemented laws for how often you need to test for Legionella. Also, the federal government has passed regulations for GSA buildings (those which are utilized for government purposes). There are stricter laws if you have had a previous Legionella outbreak, and you will need to test negative before you can operate normally again.
If you want to stay on the safe side on how often to test for Legionella in your cooling tower, once every 3 months (quarterly) is ideal. You should also account for these other listed factors and determine if it is necessary to test more often in your specific situation. You could also decide to test less frequently if you determine there is not enough of a risk and opt to do annual testing for Legionella in your cooling tower.
Chardon Labs offers Legionella testing for cooling towers, which could be scheduled regularly or as a one-time service. Chardon has several ASSE 12080 Legionella Control-certified employees. We follow ASSE, CDC, ASHRAE, and governmental guidelines as they relate to Legionella. Our core business is also chemical water treatment for cooling towers and other heating/cooling equipment that involves water. To reach out click here or give us a call at (380) 224-7395.
