Legionella in drinking water

Legionella are bacteria that occur practically everywhere in nature - mainly in freshwater environments such as lakes and streams, but also in drinking water. They are almost always present there in very low, non-hazardous concentrations. However, if these bacteria multiply, legionella can cause serious illnesses. 

The risk of contracting the disease in humans is not so much through the consumption of drinking water contaminated with legionella, but rather through the inhalation of tiny water droplets (aerosols), for example when showering or through the vapors of a whirlpool. According to the Federal Environment Agency, it is estimated that between 20,000 and 32,000 people in Germany contract legionellosis - pneumonia caused by legionella - every year. Up to 15 percent of these cases are fatal. ¹

What is legionella?

Legionella are bacteria that occur naturally in fresh water and can multiply in hot water pipes. Its name is actually derived from the term "legionnaire's disease", as the disease was first discovered in the USA at a gathering of US veterans, the "American Legion" in Pennsylvania in 1976.

There, 34 "legionnaires" fell ill with a previously unknown infection of the lungs, known today as legionnaires' disease or legionellosis. Infection in humans occurs through the inhalation of aerosols contaminated with legionella. Such finely atomized water droplets can be produced when showering, for example.

Reproduction of legionella at different temperatures

Occurrence of legionella

Legionella, which can also be found in compost or air conditioning systems, have ideal breeding conditions at temperatures between 25 and 45 degrees Celsius. They can reproduce particularly well in stagnant water. Legionella hardly reproduce above 45 °C and die off above 60 °C.

Legionella can therefore be found where warm water provides optimum conditions for their reproduction, e.g. in:

Legionella filters are therefore primarily used in:

• Showers (public or private)
• Whirlpools (public or private)
• Swimming pools
• Sports halls
• Nursing homes
• rented apartments, private households, etc.

Diseases with legionella

As pathogenic germs, legionella can cause life-threatening pneumonia (legionellosis) and other diseases. Legionnaires' disease is caused by legionella bacteria. Infection occurs through direct contact with bacteria in the form of a droplet infection, for example when the hot water mist is inhaled while showering or bathing in a whirlpool.

Legionella diseases - the most important facts in brief

Legionnaires' disease has a high mortality rate of 10 to 15 percent in proven infections. According to estimates by the Federal Environment Agency, up to 3,000 deaths per year can be assumed in Germany. There is no exact number of cases; the Robert Koch Institute assumes 1.8 cases per 100,000 inhabitants. ²

Spread and transmission via water droplets

Legionella present in Tapwater does not lead directly to a health risk, only the absorption of pathogens into the human organism through the inhalation of water containing bacteria as an aerosol can lead to an infection. This occurs, for example, via air conditioning systems or humidifiers in the home, via cooling towers or whirlpools, but also via showers, respirators, nebulizers, oxygen bubblers or in dental practices via dental units.

Legionella can grow and spread through man-made water systems - for example:

• Shower heads
• Washbasins
• Cooling towers
• Cooling systems with water fans
• Whirlpools
• Ornamental fountains and water features
• Hot water tanks and heaters
• Large, complex sanitary systems

How does a legionella infection occur?

Only in exceptional cases is an infection caused by drinking contaminated water. What is more dangerous is the water mist that can be emitted from hot water. It is used to inhale tiny particles of water, known as aerosols. If these aerosols are contaminated, it can lead to a dangerous illness. 

However, leaking pipes are also a potential source of danger. Many people become infected when traveling, for example if hygiene regulations are not observed at a vacation destination or campsite. 

The danger always comes from contaminated water. 

How does legionella get into drinking water?

The Robert Koch Institute states that water temperatures between 25 and 45 degrees Celsius are optimal growth conditions for legionella. It is particularly dangerous in water containers with stagnant water where these temperatures are reached. Deposits such as limescale and, above all, the biofilm that develops in pipes also play an important role in the development of a legionella risk. It consists of bacteria and organic substances.

The pathogens can multiply particularly well in stagnant water. Therefore, after a long absence - after a vacation - you should first drain a few liters of water when opening the tap. Experts also advise against lowering the hot water temperature of the drinking water system at home. Although this saves energy and costs in summer, it can also create ideal conditions for legionella bacteria to multiply in drinking water.

Incidents in Germany in 2020 / 2021

The German Drinking Water Ordinance ³ in its current version of March 10, 2016 stipulates a regular obligation to test for legionella. 

This applies to all contractors and other owners of drinking water installations...

• with large systems for domestic hot water heating, 
• with a commercial or public use (e.g. swimming pool), 
• and whereby the drinking water is atomized (e.g. in showers). 

Nevertheless, there are still reports of shower bans or closures of public facilities such as sports halls or swimming pools - due to an infestation with legionella. We have compiled the most important reports from 2020 and 2021 here.

Legionella infestation in Germany: press reviews 2020 & 2021

Who is particularly at risk?

Most healthy people who are exposed to legionella rarely become ill. Older people, smokers and people with weakened immune systems and chronic illnesses (e.g. diabetes) are particularly affected. Men fall ill about twice as often as women.

In general, the following people have an increased risk of illness:

• Persons aged 50 and over
• Current or former smokers
• People with chronic lung disease (COPD, asthma)
• People with a weak immune system
• People who are taking medication that weakens the immune system (e.g. after chemotherapy)
• People with cancer 
• People with diabetes
• People with chronic kidney or liver disease

How to avoid legionella in drinking water?

According to the German Drinking Water Ordinance, water samples are regularly tested in large facilities and public buildings. If a certain concentration of legionella is detected, there is a legal obligation to report this to the responsible health authority.

More illnesses generally occur in summer and early autumn than during the cold season. Nevertheless, legionella can always occur where hot water stands for too long. If you want to take precautions in your own home to reduce the spread of legionella in drinking water, you can follow the following safety measures.

• Use the water pipes regularly. 
• Avoid stagnation in the pipes.
• Avoid dead lines in the pipe system.
• Set the controller temperature on the DHW heater to at least 60 °C.
• If possible, make sure that the water temperature in the entire pipe system is above 55 °C everywhere. 

How can legionella be killed?

If legionella bacteria are already present, they can be killed by high temperatures in particular. The bacteria cannot survive at temperatures above 60 degrees Celsius. Flushing water systems in buildings with hot water is therefore an option. This method is carried out by companies that specialize in handling drinking water regulations, e.g. to protect properties. 

There are studies that show that legionella can also withstand higher temperatures over a certain period of time. For example, a study by the Helmholtz Center for Infection Research (HZI) in Braunschweig from 2015, which raises doubts about "thermal disinfection". [4] 

Another method is the use of chlorine, which, however, must be used in large quantities to effectively remove the biofilm in pipes. The safest way for consumers to protect themselves against legionella is the proper use of water filters.

Checklist: Measures in use against legionella  

Alb Filter NANO

Certified protection against legionella

Conclusion: Legionella in drinking water

Legionella are dangerous germs that pose an underestimated risk when they come into contact with water. In addition to measures prescribed by the authorities, which must be implemented by building owners, property operators and landlords, special water filters against legionella offer consumers protection.

The water filters can also have other functions, such as descaling, but they must first and foremost meet specified technical standards in order to reliably guarantee hygiene safety.

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