Although close to 100 contaminants are currently regulated by the U.S. Environmental Protection Agency (EPA) under the Safe Drinking Water Act, which requires public water utilities to test for certain contaminants and ensure drinking water supplies to exceed certain limits, there are thousands of other chemicals that are unregulated and contaminate groundwater and surface water sources, making their way into drinking water.

Taking a look at just four unregulated chemicals of concern, the Silver Spring Institute scientists analyzed data collected by EPA from 2013–2015 under its Third Unregulated Contaminant Monitoring Rule (UCMR 3) program. The dataset covered 4,815 U.S. public water systems, 27 percent of which—serving 97 million U.S. residents—had detectable levels of one or more of the following chemicals:

• 1,4-dioxane—detected in 22 percent of water systems: a solvent classified by EPA as a probable human carcinogen, which is found in consumer products
• Per- and polyfluoroalkyl substances (PFAS)—detected in 4 percent of water systems: also called “forever chemicals” due to their inability to break down in the environment or human body, PFAS are widely used in consumer products like nonstick pans and packaging, and have been associated with cancer, thyroid disease, high cholesterol, and other health problems
• Chlorodifluoromethane (Freon 22)—detected in 5.8 percent of water systems: an ozone-depleting gas previously used as a refrigerant and used in the production of fluoropolymers (e.g., Teflon)
• 1,1-dichloroethane—detected in 4.7 percent of water systems: a solvent used in paints, plastics, and pesticides, and is associated with cancer.

Underestimating and Addressing the PFAS Problem

Regarding PFAS, data collected by EPA under UCMR 3 looked for only six types (out of the thousands that exist): perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorohexane sulfonic acid (PFHxS), perfluoroheptanoic acid (PFHpA), and perfluorobutane sulfonic acid (PFBS).

Although the Silver Spring Institute study detected unregulated PFAS in only 4 percent of drinking water systems based on 2013–2015 data, more recent EPA tests, conducted as part of the Fifth UCMR (UCMR 5), using lower detection limits and accounting for 29 types of PFAS, suggest that more than 143 million U.S. residents are exposed to “forever chemicals” through their drinking water. Additionally, UCMR 5 results show that approximately 45.7 million people in states with no PFAS drinking water regulations are currently exposed to levels of certain PFAS exceeding EPA’s maximum limits, which were set in April 2024.

More specifically, in April 2024, EPA issued the first-ever national, legally enforceable drinking water standard for six PFAS known to occur in drinking water: PFOA, perfluorooctane sulfonic acid (PFOS), PFNA, PFHxS, hexafluoropropylene oxide dimer acid (HFPO-DA), and PFBS. The same month, EPA also declared two harmful types of PFAS (PFOA and PFOS) as “hazardous substances” under the Superfund Act, triggering more urgency in addressing these compounds in U.S. water.

Additionally, in February 2025, citing concerns that the Trump Administration could roll back or weaken the Biden-era EPA drinking water standards for PFAS, a bill was introduced in California that would set state-level limits for PFAS that are at least as protective as current federal standards.

Hispanic and Black Communities Disproportionately Affected

Notably, the Silver Spring Institute researchers found that public water systems with detectable levels of contaminants served counties with higher proportions of Hispanic residents (17 percent) and non-Hispanic Black residents (11 percent) than counties without (13 percent and 10 percent, respectively). The findings also build upon previous studies by Silver Spring Institute, Harvard T.H. Chan School of Public Health, and Environmental Working Group (EWG) researchers that found higher nitrite and PFAS levels in U.S. drinking water systems serving communities with higher proportions of Black and Hispanic residents.

According to Silver Spring, communities with a higher proportion of Hispanic and Black residents were more likely to be situated close to chemical pollution discharge sites, such as wastewater treatment plants, airports and military training areas, and industrial sites. Additionally, Silver Spring researchers hypothesize that, since the racial disparities in contaminated drinking water could not be explained by income or other measures of socioeconomic status, factors like historical redlining that led to the disproportionate siting of industrial facilities in communities of color could be partly to blame.