Legionella filters and protection against legionella

Legionella are bacteria that occur naturally in fresh water. In warm, stagnant water they multiply rapidly and then become dangerous. The danger comes from inhaled water mist, for example in the shower, and rarely from drinking. This guide explains what legionella are, at what temperature they die, how dangerous they can become and how a legionella filter provides reliable protection.

Legionella die off at 60 °C and above. They are killed completely at 70 °C. Their comfort zone is warm, stagnant water between 30 and 45 °C. Temperature is therefore the most important lever against their growth. The following table gives an overview of how the bacteria behave:

This results in clear values for everyday practice. The hot water cylinder should deliver 60 °C at all times. Throughout the entire pipe system, at least 55 °C is advisable. Ideally, cold water stays below 20 °C. Lowering the hot water temperature below 55 °C, for example to save energy, is considered risky from a hygiene perspective. The Umweltbundesamt (German Environment Agency) clearly advises against it.

Legionnaires' disease is fatal in 10 to 15% of cases. It is a severe form of pneumonia. Typical symptoms include coughing, chills, chest pain and headaches, as well as a high fever above 40 °C. The first symptoms appear 2 to 10 days after exposure. The illness then lasts around four weeks. A milder variant is the flu-like Pontiac fever, which subsides after about a week.

In 2019 alone, the Robert Koch-Institut (RKI) registered more than 1,500 reported cases in Germany. The number of unreported cases is higher, as many cases of pneumonia are never tested. Estimates by the Umweltbundesamt assume up to 3,000 deaths per year. People aged 50 and over, smokers and people with a weakened immune system or chronic lung disease are particularly at risk. Men fall ill about twice as often as women.

Since 2011, the Trinkwasserverordnung (German Drinking Water Ordinance) has set a technical action value of 100 legionella per 100 millilitres of water. If it is exceeded, measures are mandatory. Landlords with large-scale systems for heating drinking water must have the water tested regularly by an approved body. Tenants can request a test. Legionella are colourless and odourless, so only a laboratory sample can detect them. A temperature of 60 °C is mandatory at the storage tank outlet of large-scale systems.

Legionella reliably die at 60 °C and above. Thermal disinfection therefore uses water heated to at least 70 °C. This method and chlorination are among the measures required by the authorities in the event of contamination. For consumers, preventive steps are what count most:

• Use water pipes regularly and avoid stagnant water
• After a longer absence, let the taps run for about a minute
• Avoid dead legs in the pipe system
• Set the water heater to at least 60 °C
• Keep temperatures above 55 °C throughout the pipe system

At points of use where water is atomised, a legionella filter is an effective addition to these measures.

Around 75% of infections occur in everyday life, many of them in the shower. This is exactly where a legionella filter comes in, directly at the tap or shower head. It retains the bacteria before they get into the air as an aerosol. It makes sense wherever water is atomised: in showers, care homes, hotels, swimming pools, sports halls and when camping. In the event of a positive test result and an acute shower ban, it works immediately.

The following neutral specialist sources serve as the basis: