Nearly one-third of people across the U.S. may be exposed to unregulated contaminants in their drinking water.
Twenty-seven percent of public water systems around the U.S.—serving approximately 97 million Americans—had detectable levels of at least one unregulated chemical, according to a new paper in the journal Environmental Health Perspectives.
Black and Hispanic people were found to be more likely to have contaminated drinking water, meaning that poor water quality disproportionately affects non-white people, the study reveals.
Drinking water in the U.S. is regulated under the U.S. Safe Drinking Water Act, which is a federal law that monitors the levels of contaminants in drinking water around the country. Around 100 different substances are tested for and controlled by the Environmental Protection Agency (EPA) under the Safe Drinking Water Act, which was designed to "protect the quality of drinking water in the U.S. This law focuses on all waters actually or potentially designed for drinking use, whether from above ground or underground sources," the EPA says on its website.
However, there are a huge number of potentially harmful contaminants that are not regulated, meaning that their levels in drinking water are neither monitored nor controlled.
"We know there are thousands of other harmful chemicals that are not regulated that make their way into groundwater and surface waters, and some of these chemicals can ultimately end up in drinking water supplies," study co-author Laurel Schaider, a senior scientist at Silent Spring Institute, said in a statement.
These include chemicals such as 1,4-dioxane—a "likely human carcinogen" according to EPA—PFAS "forever chemicals", many of which are linked to cancer risk and hormone issues, chlorodifluoromethane (Freon 22), and 1,1-dichloroethane, which is also associated with cancer.
"In the early 2000s, major American chemical companies voluntarily agreed to eliminate the production of PFOA and PFOA-related chemicals. This does not mean that the production of PFAS declined," Maaike van Gerwen, the research director for the Department of Otolaryngology-Head and Neck Surgery at the Icahn School of Medicine at Mount Sinai, told Newsweek.
"On the contrary, multiple new PFAS chemicals were developed and are still being manufactured."
In the paper, the researchers describe how they analyzed EPA data from 4,815 public water systems between 2013 and 2015 and found that 27 percent had detectable levels of either 1,4-dioxane, PFAS, chlorodifluoromethane, or 1,1-dichloroethane.
Communities where high proportions of residents are Black or Hispanic were also found to be more likely to be exposed to these unregulated chemicals in their drinking water and were also more likely to be positioned close to sources of pollution, such as airports and wastewater treatment plants.
"Our findings show that the percentage of Hispanic and Black residents in a community is a consistent predictor of poorer water quality," study co-author Aaron Maruzzo, a scientist at Silent Spring Institute, said in the statement.
Previous research has also found similar patterns regarding race and pollution: one 2023 study revealed that Black and Hispanic communities had higher levels of PFAS in their drinking water, while a 2019 research paper showed Hispanic people are more likely to have high levels of nitrates in their drinking water.
High levels of nitrates in drinking water can cause methemoglobinemia—Blue Baby Syndrome—in infants, as nitrates interfere with the blood's ability to carry oxygen.
"Ultimately, we need to do a better job at protecting source waters and reducing discharges of pollutants into water bodies that feed into our drinking water supplies," said Schaider.
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References
Maruzzo A.J., A.B. Hernandez, C.H. Swartz, J.M. Liddie, L.A. Schaider. 2025. Socioeconomic disparities in exposures to PFAS and other unregulated industrial drinking water contaminants in U.S. public water systems. Environmental Health Perspectives. DOI: 10.1289/EHP14721
Liddie, J. M., Schaider, L. A., & Sunderland, E. M. (2023). Sociodemographic Factors Are Associated with the Abundance of PFAS Sources and Detection in U.S. Community Water Systems. Environmental Science & Technology, 57(21), 7902–7912. https://doi.org/10.1021/acs.est.2c07255
Schaider, L. A., Swetschinski, L., Campbell, C., & Rudel, R. A. (2019). Environmental justice and drinking water quality: are there socioeconomic disparities in nitrate levels in U.S. drinking water? Environmental Health, 18(1). https://doi.org/10.1186/s12940-018-0442-6