Regulatory Updates
What changed, what’s coming, and what to do about it — dated entries, every claim with its source. Newest first. For operators, utility managers, and consultants.
What does “10,000 mg/L TDS” mean? The USDW bright line in U.S. groundwater regulation
REFERENCEGROUNDWATER / UIC
New reference article. 10,000 mg/L TDS is not a drinking-water standard — it is the legal boundary of an underground source of drinking water (USDW) under 40 CFR 144.3. This article quotes the exact definition, explains EPA’s logic, and lists what the line decides in practice (UIC well siting, aquifer exemptions, area of review) plus three common misunderstandings.
PFAS: federal limits in force, 2026 rollback still only proposed
2024 RULE IN FORCE2026 PROPOSALS PENDING
The April 2024 PFAS MCLs — PFOA/PFOS at 4.0 ppt, PFHxS/PFNA/HFPO-DA at 10 ppt, Hazard Index 1.0 — are the law today. EPA’s May 2026 proposals (rescind four standards; push PFOA/PFOS compliance to 2031) had no final rule as of August 2026.
Running on a separate track, DoD PFAS drinking-water policy: domestic DoD-owned systems align with the federal rule (Dec 4, 2024 policy), overseas installations finish monitoring by April 26, 2027 (Sept 28, 2025 policy), and off-base private wells affected by installations got interim-action guidance July 1, 2026. If you consult for a Navy or DoD installation, check the FGS — not just the CFR.
Lead and copper: LCRI countdown to November 1, 2027 — lawsuit heard, no stay
COMPLIANCE BEGINS NOV 1, 2027IN LITIGATION — NO STAY
The Lead and Copper Rule Improvements stand as written: 10 ppb lead action level, first- and fifth-liter tap sampling, service-line inventories, and a 10-year replacement clock starting November 2027.
AWWA v. EPA (D.C. Circuit) was argued September 30, 2026 — challenging mainly the private-side service-line replacement duty — and the court issued no stay. Notably, the current EPA defended the rule. What to watch: the court’s decision (expected months after argument) could narrow whose pipes must be replaced, but the 10 ppb level and inventory deadlines rest on separate provisions.
Perchlorate: first-ever federal proposal; final rule due May 21, 2027
PROPOSED JAN 2026
EPA proposed the first federal perchlorate drinking-water standard: MCLG of 0.02 mg/L (20 µg/L), with the enforceable MCL co-proposed at 20, 40, or 80 µg/L (91 FR 398, January 6, 2026).
A consent decree (after NRDC v. Regan vacated EPA’s withdrawal) orders a final rule by May 21, 2027. If finalized, ~66,000 community and non-transient non-community systems would monitor — the first new inorganic MCL in decades, and a template for how future contaminants get regulated.
Key dates
| When | What | Status |
|---|---|---|
| 2026 (intended) | EPA final action on PFAS rescission + PFOA/PFOS 2031 extension | PROPOSED |
| April 26, 2027 | PFAS initial monitoring complete (2024 rule); OCONUS DoD PFAS monitoring complete | FINAL / POLICY |
| May 21, 2027 | Perchlorate final rule due (consent decree) | PROPOSED |
| November 1, 2027 | LCRI compliance begins: 10 ppb lead AL, inventories, replacement clock starts | FINAL LITIGATION |
| April 26, 2029 | PFOA/PFOS MCL compliance (2031 if extension finalized) | FINAL |
| 2037 | Lead service line replacement complete (10-year LCRI clock) | FINAL |
The full outlook — how-to-read labels, what your system should do now, and every numbered source — lives in one living document: Upcoming Drinking Water Regulation Changes: 2026–2029 →
Background references
Deeper explainers kept for reference — the updates above supersede them on dates and status:
LCRI: requirements and deadlines · PFAS rules: final vs. proposed
Start with the free checklist
84 self-check items across 15 rule areas — the fastest way to find your gaps.