Legionella bacteria grow in drinking water systems at temperatures between 25 and 55 °C and are transmitted through aerosolized water, for example, when inhaled while showering. An infection can lead to pneumonia requiring treatment. In Germany, approximately 1,7 cases of Legionnaires' disease per 100.000 inhabitants are reported to the Robert Koch Institute (RKI) each year. Since not all cases of pneumonia are tested for Legionella infection, it is assumed that not all cases of Legionnaires' disease are recorded. Accordingly, it is estimated that between 18 and 36 cases of Legionnaires' disease occur annually per 100.000 inhabitants. Five to ten percent of these cases are fatal.
Drinking water in residential buildings also plays a role, as the statistical evaluation of all Legionella tests conducted by Minol shows: Approximately 15 percent of the tested drinking water systems reach the so-called technical action level of 100 colony-forming units (CFU) per 100 ml of water. But Legionella poses a risk not only to health: Anyone responsible – i.e., landlords of certain properties – who violates the requirements of the Drinking Water Ordinance regarding Legionella testing faces fines of up to €25.000 or even criminal prosecution. The same consequences threaten those who disregard reporting, information, or documentation obligations – the results of Legionella tests must be kept for at least ten years. In cases of personal injury, substantial liability claims may also arise. Finally, shutting down a system due to Legionella contamination may also result in lost rental income.