We are the water experts. We track nanoplastics and microplastics alongside PFAS, and when federal PFAS drinking-water rules land, who actually enforces them at the tap matters as much as the numbers on the page. Illinois is now first in line: the U.S. EPA has tentatively approved the state for primary enforcement of the 2024 federal PFAS drinking-water rule.

On September 30, 2026, EPA published a Federal Register notice (2026-19976) giving the Illinois Environmental Protection Agency (IEPA) primary Safe Drinking Water Act enforcement responsibility for the federal Per- and Polyfluoroalkyl Substances (PFAS) National Primary Drinking Water Regulation. The Environmental Council of the States notes that Illinois is the first state to receive that designation. The determination becomes final and effective on October 30, 2026 if EPA Region 5 does not receive a timely, substantial request for a public hearing by that date.

What primacy means here

No less stringent. EPA says Illinois’ Public Water System Supervision program revisions are no less stringent than the corresponding federal PFAS regulations, so IEPA can take the lead on enforcing them for systems under state jurisdiction (not Indian Country).
State already matched the federal MCLs. On February 27, 2026, the Illinois Pollution Control Board published its identical-in-substance adoption of the 2024 federal PFAS maximum contaminant levels (MCLs) in 35 Ill. Adm. Code Part 611, covering PFOA, PFOS, PFHxS, PFNA and HFPO-DA (GenX), plus a Hazard Index that includes PFBS.
The numbers Illinois is enforcing. Illinois’ published MCLs match the 2024 federal set for those compounds, including 4 ppt for PFOA and 4 ppt for PFOS (parts per trillion), with 10 ppt levels for PFHxS, PFNA and HFPO-DA, per Illinois EPA’s September 2026 PFAS Integrated Strategy.
Clock already running for utilities. Under the state rules Illinois EPA describes: community water systems must finish initial monitoring by April 2027, compliance monitoring begins April 25, 2027, and compliance with the PFAS MCLs begins April 26, 2029.

Why the timing is unusual

In May 2026, EPA proposed keeping federal MCLs for PFOA and PFOS while letting systems seek an extra two years (into 2031) to comply, and proposed rescinding federal standards for PFHxS, PFNA, HFPO-DA and the Hazard Index mixture. Illinois has kept the broader, original 2024 package and the 2029 compliance date. A June 2026 state law (Public Act 104-0510) also blocks the Pollution Control Board from using expedited identical-in-substance procedures to adopt standards less stringent than existing Board regulations — so Illinois cannot casually track a federal rollback through that shortcut.

The water experts’ take

Primacy is operational, not symbolic. Once final, IEPA — not EPA Region 5 — is the day-to-day enforcer for covered Illinois community water systems.
Watch October 30. A substantial hearing request could delay finality; silence lets the approval take effect that day.
Federal proposals do not erase state clocks. Illinois utilities still face the monitoring and 2029 MCL milestones their state rules describe, even while Washington debates extensions and which PFAS stay on the federal list.
Know your water. Your utility’s Consumer Confidence Report and Illinois EPA’s PFAS resources are the place to see what is already measured in your system.

Hydrology University was not involved in this primacy review.

Sources

U.S. EPA, “Public Water System Supervision Program Approval for the State of Illinois,” Federal Register Vol. 91, No. 188, Sept. 30, 2026 (FR Doc. 2026-19976): federalregister.gov
Environmental Council of the States, “Illinois Receives Proposed Primacy from U.S. EPA on PFAS SDWA,” October 9, 2026: ecos.org
Illinois EPA, “PFAS Integrated Strategy,” September 2026 (PDF): epa.illinois.gov
WaterWorld, “Illinois advances PFAS drinking water primacy amid federal rule changes,” October 8, 2026: waterworld.com

Photo: Illinois State Capitol in Springfield, by PhilDaBirdMan via Wikimedia Commons (CC0). Illustration of Illinois state government; not a product endorsement.