Changes in Water Source Cause Shifts in Invertebrate Biomass, Composition, and Regrowth in a Non-Chlorinated Drinking Water Distribution System

Abstract

Invertebrates such as Asellus aquaticus, halacarid mites, copepods and cladocerans are common in drinking water distribution systems. The Zeeuws-Vlaanderen drinking water distribution system (DWDS) of Evides water company is divided into western and eastern sections, initially supplied with drinking water derived from a eutrophic reservoir (water) and groundwater, respectively. The drinking water derived from eutrophic reservoir water was characterised as less biologically stable than the drinking water from groundwater. Due to groundwater level protection measures, since 2015 the groundwater supply to the eastern section has been gradually replaced with supply from the drinking water treatment plant, which uses eutrophic reservoir water as source water. This change caused increased regrowth conditions, as observed by regulated microbial regrowth indicators (HPC22 and Aeromonas), increased invertebrate biomass, and the dominant occurrence of Asellus aquaticus, confirming observations in other Evides DWDSs. The results from the western section supplied with the same less biological stable drinking water, however, showed that the occurrence of microbial regrowth, invertebrate biomass and A. aquaticus is not only related to the biological stability of the supplied drinking water, but also to the influence of DWDS-specific conditions. The DWDS configuration as well as higher water demands in summer (western section) and/or higher sediment and Fe accumulation in the DWDS (eastern section) are suggested factors affecting regrowth and therefore subjects for further research.