Source to taps investigation of natural organic matter in non-disinfected drinking water distribution systems

Despite being reduced by treatment, natural organic matter (NOM) is ubiquitous in drinking water distribution systems (DWDSs) from sources to consumers taps where it can potentially have negative impacts on drinking water quality. While few studies have studied its behavior in disinfected and NOM-rich DWDSs, its dynamics in non-disinfected systems, characterized by low NOM content, have not been explored yet. In this study, we monitored the NOM variations occurring between sources and consumers taps of a non-disinfected DWDS using both absorbance and fluorescence, selected due to their increasing adoption by water utilities. PARAFAC analysis of fluorescence data, combined with absorbance indices, highlighted how NOM characteristics in groundwater can vary likely due to the combination of multiple factors, especially in case of shallower aquifers. The treatment processes acted differently on fluorescent components and absorbance likely due to the differences among fluorophores and between fluorescent and chromophoric molecules. Within the distribution network, variations were detected only at selected sampling locations suggesting the importance of the “last meter” factor, especially for sampling locations located within buildings. These findings remark the overall stability of water quality within non-disinfected DWDSs, but they stress the importance of localized water quality variations, suggesting several implications for DWDS monitoring and management.