Most of us assume that if something harmful were in our tap water, there would be a rule against it. For a growing class of chemicals known as contaminants of emerging concern, or CECs, that assumption does not hold. A new July 2026 report from The Water Center at the University of Pennsylvania lays out just how far the regulations lag behind the science, and the picture is a patchwork.
CECs are chemicals that are showing up in drinking water and aquatic systems faster than regulators can evaluate them. The list includes industrial solvents, tire-wear chemicals, pharmaceuticals, microplastics, and toxins from algae blooms. Many of them are persistent, mobile in groundwater, and resistant to the conventional treatment most water systems rely on. What ties them together is regulatory limbo: for the majority, there is no federal enforceable limit at all.
A federal system full of gaps
The report describes federal action as accelerating but “wholly piecemeal.” The EPA has tools it can use, including the Contaminant Candidate List that flags priority chemicals for possible regulation and the Unregulated Contaminant Monitoring Rule that requires nationwide sampling to see where these chemicals actually turn up. It has set enforceable limits (maximum contaminant levels, or MCLs) for PFAS. But for nearly everything else, the process of setting a legally binding standard is so slow that most CECs never get one. Some have sat on federal watch lists across five review cycles without a decision.
That vacuum has pushed the work down to the states, which is where the inconsistency really shows.
A state-by-state patchwork
A handful of states have stepped into the gap, and they have not stepped in evenly. California, Minnesota, and New Jersey have taken the most action, both in how many contaminants they regulate and how strict those rules are. California in particular sets the pace: it holds the most stringent drinking water standard in the country for any contaminant, a 5 parts per trillion limit on the fumigant-derived chemical 1,2,3-trichloropropane, and it created the first official definition, testing method, and monitoring program for microplastics in drinking water.
The result is that where you live largely determines what protection you get. Two contaminants, 1,4-dioxane (an industrial solvent stabilizer and probable carcinogen) and that trichloropropane, have the strongest enforceable standards spread across multiple states. New York was first in the nation to set an enforceable limit on 1,4-dioxane and even banned it above trace levels in cleaning and personal care products. Meanwhile, contaminants like lithium, the potent carcinogen NDMA that forms as a disinfection byproduct, hexavalent chromium (the “Erin Brockovich” chemical), and pharmaceuticals still lack meaningful state action almost everywhere.
Microplastics and cyanotoxins fall in between. Many states have moved on them recently, but mostly through advisories, guidelines, and monitoring rather than enforceable limits.
Why this matters in Pennsylvania
This is not an abstract or coastal problem. The report cites a joint USGS and Pennsylvania Department of Environmental Protection study that found pharmaceuticals and other emerging contaminants across PA streams used as drinking water sources, and detected at least one pharmaceutical compound in every private well sampled in central Pennsylvania, with wells near septic systems most at risk. Cyanotoxins from algae blooms, made worse by warming water and nutrient runoff, are flagged as a particular concern for rural and small water systems, exactly the kind that serve much of our region.
That last point is the hard part. Conventional treatment does not reliably remove most of these chemicals. The methods that do work, such as advanced oxidation, granular activated carbon, ion exchange, and reverse osmosis, are expensive and technically demanding to run. Those costs land hardest on the small and rural systems least equipped to absorb them, which turns a chemistry problem into an equity problem.
The takeaway
The honest summary is that the science on these contaminants is still developing, and so are the rules. Absent strong federal standards, protection is fragmented and uneven, and the communities with the fewest resources are often the most exposed. More research on health effects, treatment, and policy is needed before that changes.
Understanding where the gaps are is the first step to closing them. The Water Center at Penn’s full report breaks down ten of these contaminants one by one, with the federal status, state actions, and treatment options for each. It is a genuinely useful reference for anyone working on water access and infrastructure.
Read the full report here: Contaminants of Emerging Concern in U.S. Drinking Water (The Water Center at Penn, July 2026)
