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Legionella: Danger from the hot water tank?

Legionella are rod-shaped bacteria that are a natural component of water and pose no danger in low concentrations. Only in high numbers can they cause various symptoms in humans. But how can you protect yourself against Legionella?

How does the Legionella infection manifest itself?

The symptoms of an illness include a high fever, typical flu symptoms such as malaise or headache, but also severe pneumonia and kidney failure cannot be ruled out.

While the affected person with flu-like symptoms is healthy again within a few days, the so-called Legionnaires' disease, which is associated with pneumonia, can only be treated with antibiotics and can even be fatal.

Legionella occur in surface waters around the world and are most comfortable at temperatures between 25 and 55 ° C. They multiply fastest in stagnant waters with water temperatures of 35 to 45 ° C.

Contagion through the lungs, not through drinking

It would seem reasonable to assume that Legionella is infected by drinking contaminated water - but this is not the case. The main route of infection is through the lungs. One becomes infected with Legionella by inhaling legionella-containing water droplets in hot water, so-called aerosols.

Therefore, transmission mainly takes place where water is atomized in the air. Sources of danger for Legionella are showers and water taps as well as humidifiers and air conditioning systems, but possibly also the swimming pool with its whirlpools, artificial waterfalls, fountains and slides.

Drinking water that contains Legionella is harmless and can only lead to infection if the water accidentally gets into the windpipe. People with immune deficiencies and previous lung diseases have to be particularly careful. Smokers are also more often affected than non-smokers.

How can you prevent Legionella in the household?

Although vaccination against Legionella is not possible, there are other ways to keep it out of drinking water. As already described, Legionella occurs mainly in hot water, so it is advisable to store the service water particularly cold (below 25 ° C) or particularly hot (over 55 ° C) and always keep it in the flow. The following measures show how this can be easily achieved:

  • Instantaneous water heaters and thermal baths protect against Legionella, as they only heat the service water shortly before use. However, the flow temperature should not fall below 55 ° C.
  • In houses with water heating from a hot water storage tank, the controller temperature of the storage tank must be around 60 ° C, in the water pipes themselves no less than 55 ° C
  • Water pipes should be used regularly, otherwise the water in them will stagnate. In addition, the lines should not be excessively long.
  • Good insulation of the hot and cold water pipes reduces heat losses in the pipes.
  • Water storage tanks should not be oversized, but correspond to the actual hot water consumption
  • When visiting hotels or holiday apartments, it is best to turn on the tap and let the possibly stale water run through.
  • The installation of a water softening system can also help to reduce the risk of legionella, as soft water contains fewer nutrients for legionella.
  • All lines should flow through and have the same temperature. Hydraulic balancing can help here.

Technical measures against legionella

Thermal disinfection: To do this, all taps in the household must be opened and water at least 70 ° C flowed through for 3 minutes.

Chemical disinfection: The pipe is disinfected with chemicals. Among other things, chlorine, ozone or hydrogen peroxide are used.

UV radiation: The hot water tank is physically disinfected by UV light. This radiation has a targeted effect on the DNA of Legionella and disrupts their metabolism and reproductive ability. A hot water UV disinfection system is installed directly behind the storage tank, which continuously disinfects the water in the circulation lines.

Ultra filtration: Ultrafiltration or microfiltration is a process in which particularly small particles can be filtered out of the water, including legionella. The pores of the filter are only about 20 millionths of a millimeter wide. The filter is installed directly at the cold water inlet of the building and prevents the penetration of germs into the water pipes of the house. The process is already being used successfully in large drinking water treatment plants and some swimming pools. For private use, the technology is unfortunately extremely expensive, but very effective.

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Basically, you don't have to be afraid of Legionella in Germany. Drinking water is one of the best controlled foods in Germany. Nevertheless, caution is advised: Officially, around 600 people are infected with Legionella every year, but estimates by the Federal Environment Agency suggest that 20,000 to 35,000 people are affected by the disease.

There is a risk of legionella bacteria in particular in large buildings with extensive piping and sometimes rarely used tapping points, e.g. in hospitals, schools or hotels. Regular checks of the drinking water by specialized service providers are intended to counteract this - this is already a legal requirement for apartment buildings. Owners of one- and two-family houses can use the above information as a guide or have an inspection carried out themselves.

Don't save at the wrong end

We also advise against saving in the wrong place: Disconnected pipes, half-closed valves and lukewarm shower water from self-made solar systems can unintentionally promote the growth of legionella.

Heating systems and hot water storage tanks with modern control technology, on the other hand, can use so-called anti-legionella circuits to independently increase the domestic water to over 70 ° C several times a week and thus kill legionella in the storage tank. Therefore, the risk in the domestic household is rather low - especially with a modern heating system.

We would be happy to advise you on a new heating system with a hot water tank. Use our heating planner for a free fixed price offer including a consultation.