When you turn on the tap, you trust that someone has checked the water. And someone has — for about 90 things. The Environmental Protection Agency's National Primary Drinking Water Regulations cover a specific list of contaminants, from arsenic to uranium, that utilities must monitor and control. It is a list that has not meaningfully expanded in over two decades.
Meanwhile, industrial chemistry has not stood still. American manufacturers produce or import tens of thousands of chemical compounds. Many of them end up in our water — through industrial discharge, agricultural runoff, pharmaceutical waste, and the slow leaching of consumer products into the environment. The EPA knows many of these chemicals are present. It has health advisories and reference levels for some. But "advisory" is not "regulation," and "reference level" does not mean "enforceable limit."
The result is a growing blind spot. Your water utility may be in full compliance with every federal standard and still deliver water containing contaminants that science has linked to cancer, endocrine disruption, and developmental harm. Not because the utility is negligent, but because the law does not require them to look.
1,4-Dioxane: The Solvent Stabilizer in Your Tap Water
1,4-dioxane is a synthetic industrial chemical classified by the EPA as a likely human carcinogen. It has been used for decades as a stabilizer in chlorinated solvents and appears as a byproduct in the manufacture of detergents, shampoos, and cosmetics. It is highly soluble in water, resistant to biodegradation, and difficult to remove through conventional water treatment.
The EPA's Third Unregulated Contaminant Monitoring Rule, known as UCMR 3, collected over 36,000 drinking water samples between 2013 and 2015. The results were sobering: 1,4-dioxane was detected in 21 percent of the 4,864 public water systems tested. In 7 percent of those systems, concentrations exceeded the EPA's own health-based reference level of 0.35 parts per billion. That made it the second most frequently detected contaminant above its health reference concentration among all 28 chemicals monitored in that cycle.
A February 2025 study reinforced these findings, reporting that unregulated industrial contaminants including 1,4-dioxane, 1,1-dichloroethane, and chlorodifluoromethane were detected in the drinking water of more than a quarter of public water systems, collectively serving over 97 million Americans.
Despite all of this, there is no federal maximum contaminant level for 1,4-dioxane. No enforceable limit. No requirement that your utility test for it. A handful of states have acted on their own — New York set a limit of 1 part per billion, California requires notification above the same threshold, and Colorado adopted the EPA's 0.35 ppb reference level for groundwater. But for most Americans, 1,4-dioxane sits in the regulatory void between "known problem" and "nobody's job."
Hexavalent Chromium: The Contaminant Made Famous, Then Forgotten
In 2000, the film Erin Brockovich introduced millions of Americans to hexavalent chromium, or chromium-6, through the story of groundwater contamination in Hinkley, California, that led to a $333 million settlement against Pacific Gas & Electric. The public was outraged. Surely, people assumed, this would lead to regulation.
It did not.
Twenty-six years later, the EPA still has no specific drinking water standard for hexavalent chromium. The federal limit applies only to "total chromium" — a category that lumps together the dangerous hexavalent form with the relatively benign trivalent form — at 100 parts per billion. The EPA does not require utilities to distinguish between the two or to test for chromium-6 individually.
According to a 2022 analysis by the Environmental Working Group, hexavalent chromium contaminates tap water serving more than 250 million Americans across all 50 states, at levels exceeding what scientists consider protective of health. More recent EWG data puts the number above 260 million, served by over 7,500 utilities where the chemical has been detected. The National Toxicology Program has concluded that hexavalent chromium in drinking water causes cancer in laboratory animals, and studies have linked ingestion to stomach cancer, liver damage, and harm to children's brain development.
California finally adopted a specific hexavalent chromium standard of 10 parts per billion in April 2024. The Environmental Working Group argues that the health-protective level should be 0.02 ppb — five hundred times lower than California's new limit. For the other 49 states, the federal government has set no specific standard at all.
Pharmaceuticals and Hormones: The Chemicals We Swallow and Flush
Every day, Americans take prescription medications, over-the-counter drugs, and supplements. The human body does not fully metabolize these compounds. What remains exits through excretion and enters the wastewater stream. Conventional wastewater treatment plants were not designed to remove pharmaceutical residues, and most do not. The treated effluent — carrying traces of antibiotics, antidepressants, anti-inflammatories, beta-blockers, and synthetic hormones — flows into rivers and streams that often serve as source water for downstream communities.
The class of compounds known as endocrine disrupting chemicals, or EDCs, is particularly concerning. These include natural and synthetic estrogens, progesterone, and industrial chemicals like bisphenol A that mimic hormonal activity in the body. Studies have documented the feminization of male fish in waterways downstream of sewage discharge — a visible marker of hormonal contamination that raises questions about what chronic low-level exposure means for human health.
Antibiotic residues in water carry a different but equally serious risk. The presence of sub-therapeutic antibiotic concentrations in aquatic environments creates selection pressure that drives the development of antibiotic-resistant bacteria. The Centers for Disease Control and Prevention has identified antibiotic resistance as one of the most urgent public health threats of our time. Yet there is no federal requirement for water utilities to test for pharmaceutical compounds, no maximum contaminant level for any prescription drug, and no systematic monitoring of antibiotic resistance genes in drinking water sources.
Advanced treatment technologies — ozonation, granular activated carbon filtration, reverse osmosis — can remove many of these compounds. But they are expensive, and without a regulatory mandate, most utilities have no obligation or financial incentive to install them.
Perchlorate: Rocket Fuel in Your Water
Perchlorate is a chemical used primarily in rocket propellant, munitions, and fireworks. It dissolves readily in water and persists in the environment. At elevated levels, it interferes with thyroid function by blocking iodine uptake — a mechanism that is especially dangerous for pregnant women, infants, and developing children, for whom thyroid hormones are critical to brain development.
The EPA first determined in 2011 that perchlorate should be regulated in drinking water. Then, in 2020, the agency reversed course and withdrew that determination. In 2023, a federal court in the D.C. Circuit ruled the withdrawal unlawful in NRDC v. Regan and ordered the EPA to propose a standard. That proposed rule finally arrived on January 2, 2026 — fifteen years after the initial determination — with the EPA suggesting a maximum contaminant level goal of 20 micrograms per liter and co-proposing enforceable limits of 20, 40, or 80 micrograms per liter.
The public comment period closed on March 9, 2026. A final rule is required by May 2027 under a consent decree. Until then, perchlorate remains federally unregulated, and the current interim health advisory of 15 micrograms per liter remains non-enforceable guidance. For a chemical whose health effects have been known for decades and whose presence in water supplies is well documented, the regulatory timeline speaks for itself.
Microplastics: The Contaminant We Cannot See
Microplastics — fragments of plastic smaller than five millimeters — have been found in oceans, rivers, soil, air, human blood, and human lung tissue. They have been found in bottled water and tap water alike. And as of this writing, there is no federal requirement to test for them in drinking water and no federal standard governing their presence.
In late 2024, environmental organizations and seven state governors petitioned the EPA to include microplastics in the Sixth Unregulated Contaminant Monitoring Rule, which would cover a monitoring period from 2027 to 2031. The petition was reiterated in January 2026. The EPA's notice of proposed rulemaking for UCMR 6 was originally scheduled for August 2025 but has been delayed, with a final rule now expected in December 2026 at the earliest.
California has moved ahead independently, initiating its own microplastics testing requirements for drinking water, with monitoring phases extending through 2028. But California is an outlier. For most of the country, microplastics in drinking water remain unstudied, unmeasured, and unregulated — even as the scientific literature on their potential health effects continues to grow.
The Monitoring Gap
The EPA's Unregulated Contaminant Monitoring Rule program is the primary mechanism by which the agency collects data on emerging contaminants. UCMR 5, which ran from January 2023 through December 2025, focused on 29 PFAS compounds and lithium. As of March 2026, approximately 95 percent of the expected results have been released, with final data anticipated in fall 2026.
The program is valuable, but it is also narrow. Each five-year cycle monitors only a handful of chemicals from a universe of thousands. The lag between data collection, analysis, and regulatory action can stretch to a decade or more. And UCMR monitoring applies only to larger water systems — small utilities serving fewer than 3,300 people were not required to participate in UCMR 5 at all, leaving the communities most vulnerable to contamination with the least information.
The Bipartisan Infrastructure Law allocated $5 billion between fiscal years 2022 and 2026 to help small and disadvantaged communities address emerging contaminants, with a focus on PFAS. That funding is meaningful, but it is dwarfed by the scale of the problem. Thousands of chemicals, tens of thousands of water systems, and a regulatory apparatus that moves in five-year increments while chemistry moves in real time.
What We Believe
At the EPR Foundation, we do not believe that regulatory delay is an acceptable proxy for safety. The absence of a federal standard does not mean the absence of a health risk. It means the government has not yet acted on what the science already shows.
We believe the public deserves to know what is in their water — not just the 90 regulated contaminants, but the emerging ones that science has flagged and regulators have deferred. We support expanded monitoring under the UCMR program, faster regulatory timelines for contaminants with established health data, and greater transparency from utilities about what they test for and what they do not.
Your Consumer Confidence Report tells you what your utility found among the things it was required to look for. It does not tell you what it would have found if it had looked further. That is a gap worth closing — and it starts with understanding that compliance and safety are not the same thing.