Legionella Contamination in Warm Water Systems in Germany

Abstract

The German Drinking Water Ordinance was last amended in 2011 and tests for Legionella spp. became obligatory for warm water plumbing systems. In our study we analysed more than 135 000 water samples obtained from over 23 000 warm water systems in Germany in 2013 and 2014. Over 20 % of the water samples were Legionella positive, and in 8 % and 0.34 % of samples, respectively CFU levels were above 100 or 10 000 CFU per 100 ml, the technical values triggering reporting and decontamination measures. A significant factor influencing the level of legionella contamination is the actual water temperature at the sampling site, which should correspond to the DIN 1988 recommendations and not differ from the maximal achievable temperature of the water system conduit.