What is Legionella and how does the bacterium arise in water systems?

Legionella is a collective term for bacteria that occur naturally in aquatic environments.

In low concentrations, their presence may not pose a problem. The risk increases when the bacteria have the opportunity to grow in technical water systems, such as in properties, hotels, hospitals, spas, shower facilities, and other installations where water is stored or circulates.

Therefore, Legionella is not just about the water itself.

Temperature, stagnant water, biofilm, and the system's design all play an important role.

Short answer, what is Legionella?

Legionella are bacteria that can be found in natural and technical water environments.

The problem primarily arises when the bacteria have the opportunity to multiply in a water system and are then spread via very small water droplets, aerosols, which can be inhaled.

Therefore, showers, hot tubs, cooling towers, and other installations where water is finely dispersed are particularly relevant in Legionella prevention efforts.

How is Legionella spread to humans?

The main risk arises when water containing Legionella is finely dispersed into small droplets that can be inhaled.

This can happen, for example, during:

• Showers
• Hot tubs and spas
• Certain types of nozzles
• Cooling towers
• Other systems that produce aerosol or water mist

Drinking water is therefore not the typical route of infection for Legionella.

It is the inhalation of contaminated aerosols that is primarily relevant.

Where is Legionella found?

Legionella bacteria can occur naturally in, for example:

• Lakes
• Watercourses
• Groundwater
• Other natural aquatic environments
• There, concentrations are normally low.

When water is introduced into technical systems, the conditions change.

Pipes, tanks, water heaters, valves, and other components create surfaces where microorganisms can establish themselves.

If temperature, water turnover, and other conditions are also favorable, the bacteria can begin to grow.

Why is Legionella a problem in buildings?

A building's water system is significantly more complex than the water that enters from the waterworks.

The water passes through a network of:

• Pipes
• Water heaters
• Mixers
• Showers
• Valves
• Tanks
• Circulation lines
• Dead legs and infrequently used taps

Each such part can affect water quality.

It also means that a problem can be local.

For example, a building may have good water quality in large parts of the system, but at the same time have an area with low circulation where bacteria have better conditions to grow.

What is the importance of temperature?

Temperature is one of the most important factors when working preventively against Legionella.

Legionella bacteria can survive within a relatively wide temperature range, but growth is primarily favored in lukewarm water.

Therefore, temperature control is a central part of the design and operation of domestic hot water systems.

The principle is simple:

Cold water should be kept cold.

Hot water should be kept sufficiently hot.

Problems often arise in areas in between, where water is stagnant or where the temperature gradually changes.

Why is stagnant water a problem?

Water turnover is an important part of a hygienic water system.

When water stands still for a long time, several things can happen simultaneously.

The temperature can change.

Disinfection effectiveness can decrease.

Microorganisms have time to establish themselves.

Biofilm can develop on the surfaces.

This means that, for example, a guest room, a ward, or a shower that is rarely used can have completely different microbiological conditions than the rest of the building.

The problem is not necessarily that water has been stagnant for a few hours.

It is about long-term low water turnover and the prevailing conditions in the system as a whole.

What does biofilm have to do with Legionella?

Biofilm is particularly relevant in connection with Legionella.

Biofilm is a layer of microorganisms that adhere to a surface and are embedded in a protective structure.

It can form on the inside of, for example: 

• Pipes
  
• Tanks
• Valves
• Showers
• Heat exchangers
• Other water-carrying components
• In the biofilm, various microorganisms can live together.

This means that a water system can contain an established microbiological environment even if the water sample itself at a given time shows low levels.

This is one reason why recurring Legionella problems are sometimes difficult to solve by merely treating the water volume.

Can Legionella be found in clear water?

Yes.

Legionella is not visible to the naked eye.

Water can therefore look completely clear and still contain bacteria.

The same applies to biofilm.

A pipe does not need to look heavily soiled for microorganisms to be present on its surface.

Sight, smell, and taste are therefore not sufficient methods for assessing the microbiological status of a system.

What is Legionnaires' disease?

Legionnaires' disease is a lung infection that can be caused by Legionella bacteria. A milder version is called Pontiac fever.

Not everyone exposed becomes ill, and the risk varies among individuals.

Therefore, preventive work is particularly important in environments where susceptible individuals may be exposed, for example, in certain areas of healthcare and elderly care.

This article primarily focuses on the water system itself and the technical factors that affect the bacteria's ability to establish themselves.

Why can Legionella return after treatment?

A recurring Legionella problem can have several causes.

One important factor is that the water system itself may contain biofilm or areas with poor water turnover.

If the treatment only reduces bacteria in the water phase but does not solve the underlying problem, the bacteria may reappear later.

Examples of underlying causes can be:

• Biofilm
• Stagnant water
• Too low hot water temperature
• Too high tempered cold water
• Poor circulation
• Dead legs
• Infrequently used taps
• Complex piping systems
• It is therefore important not to ask only which disinfection method is used.

One also needs to ask why the bacteria were able to grow in the first place.

What is a dead leg?

A dead leg is a part of a piping system where water no longer circulates normally.

This can occur, for example, when a tap is removed but parts of the pipe are left behind.

The water in the remaining pipe section can then become stagnant.

Such areas can create favorable conditions for microbial growth and should therefore be identified during a review of a water system.

Can an unused shower pose a risk?

Yes, infrequently used taps are an important factor.

If a shower or tap is used very rarely, the same water remains in the pipe for a longer period.

This is particularly relevant in, for example:

• Unoccupied hotel rooms
• Holiday homes
• Office premises
• Schools during holidays
• Hospital rooms or wards with varying usage
• Properties where certain premises are periodically unused

Regular water turnover is therefore an important part of preventive work.

How is Legionella detected?

Legionella cannot be detected by looking at the water.

To assess its presence, microbiological sampling and laboratory analysis are used.

Sampling also needs to be planned in a way that provides relevant information about the system.

A single sample from one point does not always say enough about a large installation.

In case of recurring problems, it may therefore be necessary to combine sampling with a technical review of the system.

Such a review may include, among other things:

• Temperature measurements
• Circulation control
• Identification of dead legs
• Control of infrequently used taps
• Assessment of domestic hot water production
• Inspection of tanks and other components
• Assessment of potential biofilm

Can Legionella be prevented?

Yes, much of the work involves creating conditions where bacteria have less opportunity to establish themselves.

The basic principles include, among other things:

• Good water turnover
• Correct temperatures
• Functional circulation
• Minimization of stagnant water
• Regular system checks
• Cleaning and maintenance
• Control of risk areas
• Measures for microbiological deviations

The necessary measures depend on the type of facility.

Is flushing the taps sufficient?

Flushing can be an important measure to improve water turnover in infrequently used taps.

But it is not a universal solution to an established Legionella problem.

If bacteria have already established themselves in biofilm or if the system contains structural problems, further measures may be required.

Flushing should therefore be seen as part of a larger preventive effort.

Can Legionella be disinfected away?

Various methods are used to treat water systems where Legionella has been detected or where the risk is considered high.

Which method is suitable depends, among other things, on:

• System design
• Water quality
• Temperatures
• Scope of the problem
• Biofilm
• Material of the installation
• How the water is used

For larger or complex systems, the treatment needs to be designed based on the specific installation.

Chlorine and Legionella

Chlorine-based treatment is used in many types of water systems for microbiological control.

However, its effect is influenced by factors such as water quality, pH, concentration, contact time, and the amount of organic matter.

In the case of established biofilm, it can also be more difficult to reach microorganisms that are protected on the system surfaces.

It is therefore important to distinguish between disinfection of the water volume itself and treatment of a system where microbiological growth has already been established.

Chlorine dioxide and Legionella

Chlorine dioxide is also used for microbiological control in technical water systems.

One reason is that chlorine dioxide has different chemical properties than traditional chlorination and can be relevant in systems where biofilm also needs to be managed.

However, as with other treatment methods, dosage, contact time, and water quality must be adapted to the system.

There is no treatment that allows one to disregard problems with temperature, circulation, or system design.

Sanitation and preventive treatment are two different things

It is important to distinguish between two situations.

The first is that a system already has a confirmed microbiological problem.

In that case, sanitation may be needed.

The second is that one wants to reduce the risk of the problem recurring.

In that case, the work is more about long-term control.

A common working method can therefore be described as:

Step 1: Identify the problem

Find out where the problems are in the system and what factors contribute.

Step 2: Sanitize if necessary

Reduce the established microbiological load.

Step 3: Address the root cause

For example, temperature, stagnant water, or insufficient circulation.

Step 4: Maintain control

Monitor the system and, if necessary, use continuous treatment.

How does Xinix work with Legionella and water systems?

Xinix works with solutions for microbiological control of water within FreeBact®.

For larger systems, FreeBact® Dosage is particularly relevant.

FreeBact® Dosage is developed for continuous dosing in various types of water systems, from properties and industries to swimming pools, spas, and hospitals.

In the event of an existing Legionella problem, one first needs to understand the system and the cause of the microbiological load.

After that, the correct treatment strategy can be developed.

The goal should not solely be a good water sample immediately after treatment.

The goal is a stable water system over time.

Common questions about Legionella

Is Legionella a bacterium?

Yes.

Legionella is a genus of bacteria that occurs naturally in aquatic environments.

Can Legionella be found in cold water?

Yes, Legionella can also occur in cold water systems.

The risk of growth is influenced by factors such as temperature and other system conditions.

Can Legionella be found in hot water?

Yes.

Temperature is therefore a central part of preventive Legionella work in hot water installations.

Can Legionella be seen in the water?

No.

The water can look completely normal and clear even if Legionella bacteria are present.

Can Legionella be found in biofilm?

Yes.

Biofilm is an important factor as it can create an environment where microorganisms can establish and survive on the system's surfaces.

Can Legionella be transmitted by drinking water?

The primary route of infection is the inhalation of small waterborne aerosols containing bacteria, not the common consumption of drinking water.

Can an unused shower get Legionella?

Seldom-used showers and other outlets can have low water turnover, which can create more favorable conditions for microbial growth.

Does Legionella disappear if you just raise the temperature?

Temperature is an important part of Legionella control, but a complex or established problem may require further measures.

Biofilm, circulation, and the system's design also need to be considered.

Summary

Legionella is a bacterium that can occur naturally in water but can become a problem when it has the opportunity to grow in technical water systems.

Four factors are particularly important to understand:

Temperature
Lukewarm water can create favorable conditions for growth.

Stagnant water
Low water turnover gives microorganisms a better opportunity to establish themselves.

Biofilm
Biofilm can act as a protective environment for microorganisms on the system's surfaces.

System design
Blind ends, poor circulation, and seldom-used outlets can create local risk areas.

Therefore, effective Legionella work needs to encompass the entire water system, not just the water that happens to be in a single sample.

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Contact

Thanks for sticking with us until the end!
For any questions or concerns, please feel free to reach out.

Alexandra Németh, Marketing Manager, Xinix Global AB
alexandra@xinix.se
Mobile: 070-78 601 678