A multi-parametric approach is used to monitor biological stability in drinking water from a non-chlorinated distribution system in Switzerland. The method covers different aspects of microbial water quality, including microbial growth potential, abundance, and community composition.
The biological stability of drinking water implies that the concentration of bacterial cells and composition of the microbial community should not change during distribution.
Here an international research group uses a multi-parametric approach that encompasses different aspects of microbial water quality – including microbial growth potential, microbial abundance, and microbial community composition – to monitor biological stability in drinking water from the non-chlorinated distribution system in Zürich, Switzerland.
Drinking water was collected directly after treatment from the reservoir and in the network at several locations with varied average hydraulic retention times (6–52 h) over a period of four months, with a single repetition two years later.
The total cell concentration (TCC) measured with flow cytometry remained remarkably stable for water in the reservoir throughout most of the distribution network, and during the whole time period.
Conventional microbial methods like heterotrophic plate counts, the concentration of adenosine tri-phosphate, total organic carbon, and assimilable organic carbon also remained constant.
Samples taken two years apart showed more than 80% similarity for the microbial communities analysed with denaturing gradient gel electrophoresis and 454 pyrosequencing.
The only exceptions were the two sampling locations with the longest water retention times, so far for unknown reasons, which recorded a slight but significantly higher TCC compared to the other locations.
The small change in microbial abundance detected by flow cytometry was also clearly observed in a shift in microbial community profiles to higher abundance of members from the Comamonadaceae (60% versus 2% at other locations).
Conventional microbial detection methods were unable to detect changes as observed with flow cytometric cell counts and microbial community analysis.
The findings demonstrate that the multi-parametric approach used here provides a powerful and sensitive tool to assess and evaluate biological stability and microbial processes in drinking water distribution systems.
