Combat legionella pneumophila

Legionella pneumophila is a bacteria that can develop in water and cause infectious pneumonia known as legionellosis. The bacteria can be found in water sources such as hot springs, air conditioning systems, water tanks and sprinkler and watering systems.

How does Legionella form in water pipes?

Legionella can develop in water pipes when they come in contact with water with a temperature between 20-45°C. The bacteria multiply rapidly at these temperatures, especially if there is not sufficient movement and/or filtration. This means Legionella can develop in portions of the water supply system where water is stagnant, such as clogs, collection basins and storage tanks.

Other factors that contribute to the development of legionella in water pipes are:

• Biofilm: Legionella can settle in the biofilm that can form in water pipes. Biofilm is a thin, protective layer of bacteria and microorganisms that can settle on surfaces of water pipes.
• Water quality: Legionella can develop in water with high levels of organic contaminants, such as sediment and waste products.
• Warm water: Warm water supplies, such as hot water heaters, increase the likelihood of Legionella development.
• Low flow: Legionella bacteria can multiply in parts of the water supply system where water flow is slow, such as in stagnant water or collection basins.

To prevent the development of Legionella in water pipes, it is important to disinfect and filter regularly and monitor water quality.

The growth velocity of legionella

Understanding the speed of colonization is vital for risk assessment. Legionella doesn't just grow; it colonizes exponentially when the conditions are right.

• The Doubling Rate: Under ideal conditions specifically in water temperatures around 37°C to 42°C Legionella populations can double in as little as 2 to 3 hours [1].
• From Trace to Toxic: Because of this exponential growth, a system that is "clean" on Monday can reach dangerous CFU (Colony Forming Unit) thresholds by the weekend if the water stagnates [2].
• The Lag Phase: After entering a new system, there is often a short "lag phase" where the bacteria adapt. However, once they penetrate a biofilm, their growth rate stabilizes because they are no longer fighting the environment; they are feeding on it [3].

Why managing legionella is important

Taking care of water systems in factories and buildings is about more than just following rules, it is about maintaining a hygienic environment. Legionella is a type of bacteria that lives in water, but it behaves differently than many other germs.

1. The way it moves through the air 

Most water germs only cause problems if you swallow them. However, Legionella can travel in an airborne state. This happens when the bacteria get inside tiny, invisible drops of water (mist or spray) that float in the air [1].

Because these tiny drops can be carried by the wind or through air vents, the bacteria can spread far away from the water source. This makes it very important to manage systems that create mist, such as:

• Cooling Towers: Large units on top of buildings that use fans to blow out heat, often creating a light mist.
• Decorative Fountains: Water features that spray or splash water into the air.
• Misting Systems: Sprayers used to wash away germs, clean open spaces, or help keep work areas neat and healthy. 

2. Why normal cleaning often fails 

While standard cleaning methods are often effective with frequent use, Legionella can sometimes persist by hiding inside a "shield" called biofilm, a slimy layer that grows on the inside of pipes. Under certain conditions, this shield can make complete eradication difficult:

• Heat Penetration: Flushing pipes with very hot water is a common way to tackle bacteria. However, if a thick biofilm has developed, the heat may not fully penetrate the center of the slime. If the bacteria in the middle survive, they can begin to grow back once the water temperature drops. [4]
• Chemical Barriers: Standard cleaners like chlorine are effective, but they can be "used up" by the top layer of the biofilm. In cases where the biofilm is established, less of the cleaner may reach the bacteria hiding deep inside the layer.[5]

Note: These methods are much more successful when performed frequently, as they prevent the biofilm from becoming thick enough to protect the bacteria.

Places where legionella commonly grows

In the business world, Legionella likes to grow in places where water is warm or sits still for a long time.

HOCl as effective disinfectant

An excellent method of controlling Legionella pneumophila in water is to use hypochlorous acid (HOCl) as a disinfectant. HOCl is an oxidizing substance that is extremely effective in killing a wide range of bacteria and viruses, including Legionella pneumophila. It is a safe and environmentally friendly option and does not cause byproducts such as trihalomethanes, which can be harmful to health. It is important to determine the proper concentration level of HOCl and treat the water long enough to kill the bacteria. HOCl can be an excellent option for places where chlorine cannot be used, such as drinking water systems for livestock.

On-site generation with the Watter system

The Watter System is an in-situ disinfection technology. In-situ is Latin for on-site. By producing your disinfectant on site yourself, you thereby eliminate a number of links in the process, by making purchase, storage and transport of the normally hazardous substances unnecessary. A big step forward in sustainability! And because our system, through electrolysis, produces the disinfectant using water and salt as raw materials, the process is more environmentally friendly and sustainable than other disinfection methods.

References

1. CDC. “How Legionella Spreads.” Legionella (Legionnaires’ Disease and Pontiac Fever), 24 Apr. 2024, www.cdc.gov/legionella/causes/?CDC_AAref_Val=www.cdc.gov/legionella/about/causes-transmission.html.
2. CDC. “CDC Archives.” Cdc.gov, 2024, https://archive.cdc.gov/#/details?url=https://www.cdc.gov/vitalsigns/legionnaires/index.html
3. Environmental Protection Agency. (2016). Technologies for Legionella control in concentrated building water systems (EPA 810-R-16-001).https://www.epa.gov/sites/default/files/2016-09/documents/legionella_document_master_september_2016_final.pdf
4. Pecastaings, B. J., Bertholon, I., Segonds, C., Martini, C., & Roques, C. (2010). Development of heat-shock resistance in Legionella pneumophila modeled by experimental evolution. Applied and Environmental Microbiology, 76(24), 8101–8106. https://doi.org/10.1128/AEM.00162-10
5. SHP Wassertechnik GmbH. (2025, March 25). Biofilms in drinking water systems – challenges and measures. https://shp-wassertechnik.de/en/information-centre/expertise-shp-wassertechnik/biofilms-in-drinking-water-systems-en