Microbial Characteristics of Water Distribution: Compiled Investigations in a German Drinking Water Distribution System

In the last few years microbial activities within the drinking water distribution network have gained more and more attention. Hygienic problems, harassment with odor and bad taste, and even material deterioration are the consequences of microbial life in the pipes. The growth of adhesive bacteria, so-called biofilms, seems to be the main reason for the problems mentioned above. Bacteria settling down as biofilm develop specific characteristics concerning persistence, increased metabolic activities, and sheltering opportunistic microbes. Moreover, biofilms are difficult to detect and to identify by conventional microbiological methods. In the distribution network of a German city biofilms were sampled and characterized by sensitive molecular biological and biochemical techniques. The correlation between different pipe materials and biofilm growth could be followed up over the time. The source and quality of the raw water influenced the population diversity as well as the metabolic activity of the biofilms. Opportunistic and pathogenic bacteria such as enterococci, mycobacteria, and legionellae were obviously sheltered and may persist within the biofilms, even though rarely. The specific characteristics of biofilms increased the tolerance to disinfection steps and initiated the microbial stress and repair responses. Besides that, a horizontal gene transfer between different biofilm bacteria has to be considered as potentially risky, especially with surface water as a raw water source. As a conclusion, monitoring of biofilms in distribution networks is technically as important as conventional hygienic control to avoid harassment and to manipulate inevitable biofilms to support good water quality.