Enterococci in drinking water systems

Colonies of enterococci on nutrient agar

in recent years, enterococci have been detected more frequently in drinking water, which often resulted in a boil water notice. The aim of the project is to improve the understanding of the contamination and behaviour of enterococci in drinking water systems and use this to make recommendations on the evaluation of findings and on measures to avoid reputational damage to water supply companies.

Enterococci in drinking water systems – presence, propagation, disinfection

For many years, intestinal enterococci have been considered indicator organisms that provide a clear indication of faecal contamination in drinking water. In the German Drinking Water Ordinance, enterococci, as a microbiological parameter, are equated to the parameter Escherichia coli  (limit value of 0 per 100 ml). Since 2018, enterococci have also been analysed in every microbiological drinking water test.

Swift action is needed if enterococci are detected in drinking water samples. For sustainable recommended actions to avoid positive enterococci findings in drinking water systems, firstly, the possible causes of these positive findings must be clear and secondly, information needs to be available on the behaviour of enterococci in drinking water. The research project therefore focused on the following issues:

  • Can enterococci multiply in drinking water?
  • Can enterococci persist in drinking water systems (e.g. in sediments or biofilms)?
  • Which species of enterococci are found in drinking water systems?
  • Is there an increased resistance of environmental isolates to chemical disinfectants (chlorine, chlorine dioxide) or to UV disinfection?
  • Which habitats outside of warm-blooded animal intestines are colonised by enterococci?
  • In which invertebrates can we find enterococci?


Hügler, M., Petzoldt, H., Reitter, C., Hambsch, B.: Zunehmende Befunde von Enterokokken im Trinkwasser [Increasing evidence of enterococci in drinking water]. Veröffentlichungen aus dem Technologiezentrum Wasser [Publications from TZW], Volume 85, p. 153-166 (2018)