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May 2, 2019

Recent news articles on the quality of California’s tap water, based on the Environmental Working Group’s (EWG) commentary published in the journal Environmental Health, were alarmist and misleading. The commentary attempted to apply a cumulative risk framework to drinking water contaminants in the state, but misrepresented the public data.

For context, a commentary is meant to provide perspectives, insights, and criticisms to, typically, one research article and to highlight possible areas for future research. Though EWG’s commentary has been presented in the media as a “study” it is not as it does not include any methodology nor true results as one would see in a peer-reviewed study published in a scientific journal.

The commentary does not offer new insights into the quality of California’s drinking water, but simply shuffles through long-public data of contaminants that are known to be present in water in extremely low levels. Along this same line, the article’s idea of cumulative risk in drinking water is not novel, but instead builds off of two existing studies within the drinking water community.

The first, a report released in 2014 by the Water Research Foundation (WRF), Identifying Meaningful Opportunities for Drinking Water Health Risk Reduction in the United States, summarized the foundation’s work to develop the Relative Health Indicator (RHI) Calculator. This calculator is meant to be used by utilities to help identify contaminants in treated drinking water that may pose the highest remaining health risk in order to help utilities prioritize health risk reduction strategies.

This work continued through a second study cited by EWG, Using a relative health indicator (RHI) metric to estimate health risk reductions in drinking water by Alfredo et al. (2017), which furthered the use of the RHI calculator by modifying the formula and recommending it be used for regulatory and policy decision-making.

The Association of Metropolitan Water Agencies and its members support the ongoing work that WRF and others have done to progressively develop methods to help prioritize the health risks for various chemical and microbial contaminants that can be found in drinking water in the United States. This is vital work that will help push the sector forward allowing for better ways to prioritize limited resources. AMWA members remain committed to protecting public health by providing safe and reliable drinking water to their customers.


The Association of Metropolitan Water Agencies is an organization of the largest publicly owned drinking water suppliers in the United States.

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