Household-Level Variability of Nontarget Analytical Results for Drinking Water Provides a Tool for Uncovering Constituents Introduced by Distribution System Components

The variability in the nontarget chemical composition of tap water from 120 households and 15 brands of retail water was analyzed during two seasons. Fifteen households in eight separate community water systems were evaluated with the goal of identifying compounds with high within-source variability and investigating potential origins of the observed variation. High resolution mass spectrometry with liquid and gas chromatography was implemented and 10 chemical features from each water system with the highest coefficient of variation and a tentative library match were prioritized for investigation. This prioritization filter reduced the number of considered features from the 16,929 originally isolated to 282. High confidence structural annotations could be assigned to 134 compounds, which were then categorized based on plausible contaminant inputs. The most common source category was plastic (potentially originating from piping, fittings or packaging), with 47/50 of the GC compounds and 22/40 of the LC compounds having possible plastic-related origins. Other important source categories included other distribution system components (polychlorinated biphenyls, historically used in caulking), disinfection byproducts (trihalomethanes), and contaminants present in source waters at varying levels (sucralose, PFAS). The findings highlight the diverse constituents introduced into drinking water from the distribution system and the importance of assessing chemical exposures via drinking water at the point of use.