Private, public, and bottled drinking water: Shared contaminant-mixture exposures and effects challenge

Humans are primary drivers of environmental-contaminant exposures worldwide, including in drinking-water (DW). In the United States, point-of-use DW (POU-DW) is supplied via private tapwater (TW), public-supply TW, and bottled water (BW). Differences in management, monitoring, and messaging and lack of directly-intercomparable exposure data influence the actual and perceived quality and safety of different DW supplies and directly impact consumer decision-making.

The purpose of this paper is to provide a meta-analysis (quantitative synthesis) of POU-DW contaminant-mixture exposures and corresponding potential human-health effects of private-TW, public-TW, and BW by aggregating exposure results and harmonizing apical-health-benchmark-weighted and bioactivity-weighted effects predictions across previous studies by this research group.

Simultaneous exposures to multiple inorganic and organic contaminants of known or suspected human-health concern are common across all three DW supplies, with substantial variability observed in each and no systematic difference in predicted cumulative risk between supplies. Differences in contaminant or contaminant-class exposures, with important implications for DW-quality improvements, were observed and attributed to corresponding differences in regulation and compliance monitoring.

The results indicate that human-health risks from contaminant exposures are common to and comparable in all three DW-supplies, including BW. Importantly, this study's target analytical coverage, which exceeds that currently feasible for water purveyors or homeowners, nevertheless is a substantial underestimation of the breadth of contaminant mixtures in the environment and potentially present in DW. Thus, the results emphasize the need for improved understanding of the adverse human-health implications of long-term exposures to low-level inorganic-/organic-contaminant mixtures across all three distribution pipelines and do not support commercial messaging of BW as a systematically safer alternative to public-TW. Regardless of the supply, increased public engagement in source-water protection and drinking-water treatment is necessary to reduce risks associated with long-term DW-contaminant exposures, especially in vulnerable populations, and to reduce environmental waste and plastics contamination.