Tower Tech Cooling System

Written by Jignesh Shah
cooling tower water treatment

What is Legionella?

Legionella is bacteria that are found to naturally occur in freshwater sources. They are found in water bodies like rivers and lakes generally in low amounts and therefore do not lead to diseases.

Contaminated water building systems or cooling towers are responsible for most Legionnaires’ outbreak. Legionnaires’ disease is a serious and potentially fatal illness caused due to Legionella found in water.

Legionella can sneakingly grow under varied circumstances and multiply to dangerous levels under certain conditions. You may think that your cooling tower systems are clean and well-treated, but you will notice with time; that how even seemingly minor disruptions can rapidly turn into a chance for Legionella to set up and spread at an alarming state.

Things inside the cooling towers that lead to legionella growth

Various factors become a cause of legionella growth in cooling towers and can become a breeding ground for it. Some of the common causes are as follows:



The scale is a hard, rock-like buildup in your cooling water systems which grows there because of the minerals from the water collected inside your water system. A barrier is created because of scale build-up, which interferes with the efforts of heating or cooling the water, this can lead to unpredictable or unacceptable water temperatures. Legionella and other germs proliferate due to scale build-up in the cooling water systems.


Sediment is the collection of minerals and natural material broken down by processes of erosion. It grows in unfiltered water that is not properly treated and also compromises the heating and cooling systems. When sediment builds up, it brings germs with it that are hard to discard. This leads to more germ build-up including legionella, sediment lets it grow in its protected environment.


It is essential to maintain a required level of pH balance in the industrial cooling towers. Even the disinfectants are proactive if the pH level of the water is between 6.5 and 8.5. The chemicals, changes in the environment due to pollution, and the amount of plant or organic material in water influence changes in the pH level of water.

Water temperature Variations

The best possibility of legionella growth in water is when the water temperature is at 77 to 108 degrees Fahrenheit. However, legionella can still build up in temperatures outside this range. Some factors increase the risk of having legionella-friendly temperatures such as:

  • Stagnant water
  • Setting water heater too low
  • Coldwater pipes exposed to hot weather
  • Places in cooling towers where cold and hot water may mix
  • Long pipes losing heat with the flowing water
  • Having cold and hot water pipes too close together


Biofilm is a thin film of mucus that can grow on any surface that is exposed to moisture continuously. This sneaky build-up eats up disinfectant, which leaves an ideal environment for Legionella growth. Biofilm is not easy to get rid of, it can stay on the surfaces of your cooling water systems for years and even decades.


When water is stagnant, it gives an opportunity to biofilm for growth and soaks up more than its fair share of disinfectant. The reasons for stagnant water may vary like when water usage is decreased or certain fixtures go unused. The pipes that have low to no flow of water can give a rise to Legionella growth.

Changes in water pressure

When water pressure in the water systems changes for any reason, it displaces biofilm and spreads its germs into the entire water system, which leads to Legionella growth somehow.

water cooling towers

Lack of disinfectant

Adding disinfectants to your water systems help keep it germ-free, but sometimes even an adequate amount of disinfectant uses up its germ-killing powers super-fast, which ultimately leaves the water system vulnerable to Legionella. Some processes like heating, storing, and filtering water can play disinfectant-hogs.

Things outside the cooling towers that lead to legionella growth

Municipal water supply

Even the minor changes in the municipal water supply can raise the amount of sediment in the water, affect disinfectant levels, and cause dreadful changes to pH levels as well. This highly affects your fight against Legionella in your cooling towers.

Water main breaks

Water main break results in bringing in extra dirt and undesirable matter which uses up the disinfectant supply and further compromise your water. Moreover, water main breaks are responsible for sudden changes in water pressure that have the ability to knock any biofilm out of its place.


Quavering due to construction can dislodge scale and biofilm; and along with it, dislodges the Legionella living in it into the water.

How to prevent legionella before it takes place?

Some of these factors are not in your control, unfortunately. Having said that, there are still some ways you can put up with these issues. You have to have a solid water management program in your industry. You can get in touch with your cooling tower manufacturer as well who will proactively help you address these issues before Legionella goes out of control.