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.