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February 23, 2018

How many U.S. residents are exposed to unsafe drinking water each year? Up to 45 million, a new study estimates.

Daily Briefing

    Tens of millions of U.S. residents might have been exposed to unsafe drinking water from 1982 to 2015, according to a study published Monday in the Proceedings of the National Academy of Sciences.

    Study details

    For the study, researchers reviewed data from the Environmental Protection Agency (EPA) on 17,900 community water systems in the continental United States to identify violations of health standards enacted under the federal Safe Drinking Water Act (SDWA). The researchers focused on violations that occurred from 1982 to 2015.

    The researchers examined a range of violations, from the presence of coliform bacteria—which is easily detected and serves as an indicator of general bacterial contamination—to elevated lead levels. The violations did not all pose immediate health risks, but water contaminants could lead to short-term illnesses, such as acute gastroenteritis, and chronic conditions, such as cancer and neurological disorders, USA Today reports.

    The researchers then combined the data with U.S. census information, such as average household income and housing density, to determine what factors made communities the most vulnerable to SDWA violations.


    According to the study, between 3% and 10% of U.S. community water systems had health-based SDWA violations in a given year from 1982 to 2015. As a result, the researchers estimated between nine million and 45 million U.S. residents might have been exposed to unsafe drinking water each year over the 34-year period. In particular, the researchers found nearly 21 million U.S. residents in 2015 might have been exposed to unsafe drinking water from community water systems with health-related SDWA violations.

    The researchers found the number of health-related water quality violations rose during the study period, with surges in such violations occurring in the years following the implementation of a new regulation. For example, the researchers found that within five years of a new rule regarding coliform being enacted in 1990, the number of SDWA violations doubled. In another example, the study found that health violations spiked in rural areas in the 2000s after the EPA issued regulations intended to limit the presence of disinfectant byproducts in community water systems.

    The researchers also identified violation hot spots—where communities had repeat health-related violations—in several states, particularly in the country's Southwest region. According to the study, more than one-third of community water systems in Idaho, Nebraska, and Oklahoma had health-related water quality violations in multiple years during the study's period.

    In addition, the researchers said community water systems in West Texas had repeated violations over the past decade. The researchers said repeat violations indicated that water systems in the regions faced recurring issues.

    Further, the researchers found certain communities were more vulnerable to potentially unsafe drinking water. For instance, the researchers found water systems in rural areas were more likely to experience health-based quality violations than water systems in urban areas. The researchers also found that community water systems serving minority and low-income communities were more likely to violate regulations regarding coliform bacteria, which often accompanies disease-causing pathogens.

    The researchers found larger water systems typically had fewer violations than smaller systems, and privately owned water systems typically had fewer violations than publicly owned systems. As such, the researchers found smaller communities that purchased treated water from larger water systems—particularly privately owned systems—had fewer violations than larger communities that relied on smaller or publically owned systems.


    Maura Allaire, the study's lead author and a water economist at the University of California-Irvine, said the United States in general "has really safe water," and spikes in health-related violations do not mean U.S. water has become less safe over the years. However, she said surges in violations of health-related standards do reflect a shift in the accepted levels of a contaminant in community water systems. Allaire said the study is intended to help policymakers identify which parts of the United States might need assistance with meeting national water standards or further scrutiny.

    Kristi Pullen Fedinick—a scientist with the Natural Resources Defense Council, which in 2017 published a nationwide survey on SDWA violations—said the study might underestimate the extent of problems facing the United States' water systems, because "[o]n a national scale … there's a huge amount of underreporting" (Rice, USA Today, 2/12; Langin, Science Magazine, 2/12; Plumer/Popovich, New York Times, 2/12; Allaire et al., Proceedings of the National Academy of Sciences, 2/12).

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