Small numbers of bacteria such as Legionella enter the water supply. In drinking water systems within buildings, technical water systems or swimming pools, they often find favorable conditions for their survival and reproduction. These conditions include temperatures between 25°C to 45°C, stagnating water and nutrients. Some types of bacteria form biofilms, which in turn provide a habitat for other bacteria.

 

Some of these water bacteria pose a health risk to humans, e.g. Legionella, Pseudomonads, E.coli or Salmonella. According to the World Health Organization (WHO), Legionella represent the greatest health threat to humans. By inhaling contaminated aerosols (e.g. when showering), they can cause legionellosis. The dangerous Legionnaires' disease or the milder Pontiac fever are well known diseases. The number of Legionella cases is increasing drastically year after year.