Why do bacteria form in stored water


Legionella: Danger from the shower head

Saving energy when heating water also has its downside. If you reduce the temperature of your hot water storage tank to save energy, you run the risk of creating a dangerous concentration of legionella. Drinking water is subject to the strictest hygiene regulations in Germany, but according to the Federal Environment Agency it contains germs. Including Legionella, but in concentrations that are harmless to health. However, those who regulate their hot water below 60 ° C ensure the best conditions for these bacteria. They feel most comfortable at temperatures between 25 and 55 ° C. They multiply fastest in standing water (reservoir) with water temperatures of 35 to 45 ° C.

Information from the Federal Environment Agency

“In the public pipeline network of the water supply company (WVU), the water temperature is well below 20 ° C, which effectively prevents bacterial growth. Up to the water meter in buildings, the water suppliers usually deliver very good drinking water quality, which is regularly monitored and confirmed by the health department. After the transfer point of the drinking water in the buildings, the operator of the drinking water installation, i. H. usually the house owner to ensure that the drinking water does not deteriorate on its way from the water meter to the tap and that the limit values ​​and requirements of the TrinkwV 2001 [drinking water ordinance] are adhered to. "

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This is how legionella can be avoided

Worksheet W 551 of the German Gas and Water Association (DVGW) makes the following requirements:

  • The drinking water at the outlet of the water heater must be at least 60 ° C. Since there is a high water exchange in the hot water storage tanks of one and two-family houses, an outlet temperature of at least 50 ° C is permissible here.
  • In order to maintain a minimum temperature of 60 ° C, the installation of a so-called "legionella switch" is recommended. With this circuit, the content of the water tank is heated at regular intervals (usually briefly to over 70 degrees).
  • If the pipeline content between the water heater and the tapping point is more than three liters, circulation lines must be installed. Circulation pipes keep the water moving and avoid longer downtimes. However, the water in the circulation line may cool down by a maximum of 5 ° C.
  • Also be careful with cold water: If cold water is in the pipeline for a longer period of time, it can heat up to over 30 ° C, for example through neighboring heating pipes.
  • With the use of decentralized instantaneous water heaters, the legionella risk can be greatly reduced. The heated water is not stored here before it is withdrawn.

Contagion through the lungs, not through drinking

It would be obvious to assume that Legionella is infected by drinking the water. But that's not the case! The main route of infection is through the lungs. You become infected with Legionella by inhaling water droplets containing Legionella in hot water, i.e. when showering, on taps or in whirlpools. Drinking water containing Legionella, on the other hand, is harmless and can only lead to infection if the water accidentally gets into the windpipe.

Severe flu symptoms

Doctors assume that Legionella is responsible for around 15,000 to 30,000 Legionnaires' diseases per year. The most important forms of legionnaires 'disease are Legionnaires' disease and Pontiac fever. Legionnaires' disease is a form of pneumonia and usually begins with chest pain, headaches, coughs, chills and a high fever. This type of pneumonia is often severe and lasts about four weeks. In about one in ten people affected, it is even fatal. With Pontiac fever, the course of the disease is not so severe. The disease runs like the flu: fever, malaise, headache, limb pain, chest pain and cough. The disease usually goes away on its own within two to five days.

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Tags:Hot water, water heating