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Determining the Prevalence of Contaminants in Treated and Untreated Drinking Water

Image of a stream contaminated with chemicals with an image of faucet filling up glass Just 2.5 percent of the Earth’s water is fresh, making it crucial for humans to use water in smart, effective ways that preserve this precious resource. Water reuse has become an important part of the solution. In the United States, wastewater is treated and may then be discharged into surface water or ground water aquifers. There, natural processes including volatilization, dilution, sedimentation, and reactions to sunlight may decrease the concentration of contaminants before the water is taken up for further treatment in drinking water facilities.

Although wastewater and drinking water treatment is designed to remove pollutants, there is potential for trace levels of unregulated contaminants to be present in treated drinking water. Improvements in analytical instrumentation now allow scientists to measure these very low concentrations. There is an emerging awareness of the potential for these chemicals to be present in every portion of the water cycle—wastewater, surface water, groundwater, and drinking water. To develop strategies for protecting human health, EPA needs to understand the prevalence of contaminants in both treated drinking water and its source water.

Scientists from EPA and the U.S. Geological Survey (USGS) conducted a multi-phase study to determine the presence of contaminants of emerging concern (CECs) in treated and untreated drinking water collected from approximately 25 drinking water treatment plants (DWTPs) across the United States. Samples were analyzed for 247 chemical and microbiological pollutants, including a wide range of chemicals used in homes, businesses, and industries. Treatment plants chosen for this study receive waters impacted by a variety of waste sources, including municipal waste, septic systems, and livestock production.

The contaminants examined in the study are not regulated in drinking water by EPA, and little is known about their prevalence. The samples were analyzed by 15 methods for chemicals, microorganisms, and estrogen bioactivity. Analyte selection was focused on pharmaceuticals, but also included other classes of analytes, including per- and polyfluoroalkyl substances (PFAS), hormones, fungi, bacteria, protozoa and viruses.

The studies provide important baseline information on the presence of contaminants in treated and untreated drinking water, as well as qualitative information on the efficacy of differing drinking water treatment technologies in removing contaminants. The results will be used to inform the next generation of EPA drinking water safety standards.

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