Poorly maintained cooling towers can become breeding grounds for Legionella bacteria, which cause Legionnaires’ disease, a serious lung infection. This bacterium thrives in warm, stagnant water. If water in the tower becomes contaminated and turns into mist, people nearby can inhale it and get sick.
In 2024, a cooling tower in Melbourne was linked to 114 confirmed cases of Legionnaires’ disease and two deaths. That incident is a reminder of what can happen when cooling tower maintenance is ignored.
In this post, we’ll look at why Legionella in cooling towers is a serious concern, what increases your risk, and how to prevent Legionnaires’ disease before it starts.
Why Legionella Control in Cooling Towers Is Critical
Legionnaires’ disease is a dangerous lung infection you get from breathing in water droplets contaminated with Legionella bacteria. You can’t catch it from another person; it’s spread when mist from things like showers, hot tubs, or cooling towers gets into your lungs.
Cooling towers are a concern because they reuse the same water, making them an ideal environment for Legionella to grow. If you don’t keep up with maintenance, that contaminated water can turn into mist and affect anyone nearby, your staff, residents, or people passing by.
Several U.S. cities experienced outbreaks in 2024 that were traced to cooling towers, highlighting the importance of regular water testing and a comprehensive prevention plan. In one New Hampshire case, skipping routine checks for months resulted in multiple individuals getting hospitalized.
Top Risk Factors for Legionella Disease in Cooling Towers
Source Water Quality
If you’re starting with water that already contains a lot of contaminants, it makes the job harder from the outset. Things like dirt, organic matter, or high bacteria can bring germs into your system. Pre-treating and filtering your water should be the first step when preventing Legionella in cooling towers.
Ineffective Water Treatment
Chemical dosing needs to be steady and accurate. If biocide levels are too low or too high, you create an environment where Legionella can grow. It’s important to monitor your biocides and corrosion inhibitors to make sure your water remains safe and your equipment is protected from rust and buildup.
Inadequate Disinfection Practices
Cleaning your system once a year isn’t enough. Cooling tower maintenance should include routine disinfection, whether that involves occasional chemical shock treatments or steady, low-level dosing. Some places also use UV disinfection as an extra step.
Biofilm Formation
Once biofilm forms, it acts as a protective shield, letting bacteria remain even when high doses of chemicals, such as chlorine or bromine, are used. The only way to effectively eliminate biofilm is by thoroughly scrubbing surfaces and closely monitoring your chemical levels.
Cooling Tower Design & Materials
Older cooling towers, or those built with materials that let scale or microbes build-up, put your system at higher risk. Newer models, designed with antimicrobial surfaces and improved drainage, make it harder for Legionella disease to take hold in cooling towers.
Spray Drift and Aerosolization
Drift happens when tiny droplets escape into the air. If those droplets contain Legionella, they can travel long distances. Drift eliminators help keep most of that contaminated mist from escaping into the environment.
How to Prevent Legionnaires’ Disease in Cooling Towers
Routine Cooling Tower Maintenance
Follow a routine maintenance schedule. Clean the basins and nozzles, inspect for scale, test the water, and make sure your chemical treatments are effectively controlling bacteria and buildup. A cooling tower maintenance checklist helps you remember every step, so nothing gets overlooked.
Regular Inspections and Monitoring
You’ll get the best results if you check your system every week or month (depending on how much you use it). Write down numbers for things like temperature, chemical levels, and flow rates. Keeping a log makes it easy to spot problems early and show inspectors that you’re following all the safety rules.
Legionella Testing Protocols
Test for Legionella bacteria in your cooling towers at least every three months. If your building has a lot of water use or serves vulnerable people, plan to do these tests more often. Always use certified labs so you can trust your results and keep your water system safe.
Implementing a Water Management Plan (WMP)
Both ASHRAE Standard 188 and the CDC recommend having a Water Management Plan for your building and its systems. A WMP outlines how your system operates, who is responsible for each maintenance task, and what to do if Legionella disease is detected in your cooling tower.
Questions to Ask: Are You at Risk for a Legionella Outbreak?
- Do you have a formal water safety plan?
- When was your last Legionella test?
- How regularly do you clean and inspect your system?
- Are you following the right steps for biocide treatment?
If you’re unsure about any of these, now’s the time to review your prevention plan.
Cooling Tower Legionella Prevention Tips
- Flush out any stagnant water if your system hasn’t been used much lately.
- Scrub basins, nozzles, and drift eliminators to keep bacteria and buildup away.
- Use real-time monitors to detect changes in water quality or chemical balance immediately.
- Check your drift eliminators regularly, replace them if they’re worn out or not working effectively.
- Each month, double-check your chemical dosing system to keep it running smoothly.
Regulatory Compliance & Standards to Follow
- ASHRAE Standard 188 – How to manage risks in building water systems.
- CDC Legionella Toolkit – Step-by-step guide to prevent Legionella.
- OSHA Technical Manual Section III: Chapter 7 – Legionella guidance and rules.
If you don’t follow these requirements, you could face fines, be forced to shut down, or even get sued, if an outbreak is linked to your site. Keep thorough records of all maintenance, tests, and repairs to show you’re staying on top of your responsibilities when an audit comes around.
Frequently Asked Questions
Q1: How often should cooling towers be tested for Legionella?
At least every 3 months, high-risk facilities may need monthly testing.
Q2: What chemicals kill Legionella in cooling towers?
Chlorine dioxide, bromine, and isothiazolin are common and effective biocides.
Q3: Can Legionnaires’ disease be prevented entirely?
With routine cooling tower maintenance, regular testing, and strict compliance with safety guidelines.
Final Thoughts
Preventing Legionella isn’t just about checking off boxes; it’s about keeping people safe. With regular inspections, water testing, and a clear, consistent water management plan, you can make an outbreak much less likely and keep your cooling system running safely.
Don’t leave your cooling system to chance. Call now or Reach out to our team for a Legionella risk assessment or to talk about your water management needs.
