Methods and data sources

• Systems and violations: EPA SDWIS via the ECHO SDWA bulk download, snapshot 2026Q3, updated quarterly. Active community water systems only. Violations whose noncompliance began on or after Oct 1, 2021. Counts use distinct violation IDs (enforcement rows are de-duplicated).
• PFAS: EPA UCMR 5 occurrence data. For each chemical we average results at each sampling location (non-detects = 0) and use the highest location average, approximating the rule’s running annual average. Compared to the April 2024 PFAS rule: PFOA and PFOS 4.0 ppt (enforceable; MCL compliance by April 26, 2029); PFHxS, PFNA, HFPO-DA (GenX) 10 ppt and Hazard Index 1.0. Status as of Oct 2026: on May 18, 2026 EPA proposed to rescind the PFHxS/PFNA/GenX/Hazard Index limits (Federal Register) and to let eligible systems request PFOA/PFOS compliance extensions to April 26, 2031 (EPA). Neither proposal is final; the 2024 limits remain on the books. We weight PFOA/PFOS more heavily than the four PFAS proposed for repeal.
• Lead/copper: latest 90th percentile reported in SDWIS, compared to today’s 15 ppb lead and 1.3 mg/L copper action levels. EPA’s Lead and Copper Rule Improvements (final Oct 30, 2024; effective Dec 30, 2024) lower the lead action level to 10 ppb (0.010 mg/L) with a compliance date of November 1, 2027 (40 CFR § 141.80). LCRI eliminated the old 10 ppb “trigger level”; 10 ppb is the new action level. We flag systems above 10 ppb before that date as a heads-up. Verified against the e-CFR and Federal Register.
• ZIP matching: (1) EPA Community Water System Service Area Boundaries (v2): a ZIP is linked when its Census ZCTA center falls inside the service area, or for small areas the nearest ZCTA center; (2) ZIPs served listed in UCMR 5 and SDWIS; (3) fallback: the utility’s mailing-address ZIP (flagged). Out-of-state UCMR ZIPs are dropped.
• Grade (A–F): points = 10 per health-based violation (max 40) + 1 per other violation (max 10) + 12.5 per PFOA/PFOS location-average over 4 ppt (max 25) + 5 per other PFAS over its 2024 limit or Hazard Index over 1 (max 10) + 20 if lead is above the current 15 ppb action level. A <5, B <15, C <35, D <55, F ≥55. This is our own heuristic, not an EPA rating.
• Filter matching: maps contaminants to NSF/ANSI standards (42, 53, 55, 58). Always confirm the product’s certification lists that specific contaminant. Product links are placeholders until affiliate accounts are live; grades are never sold.
• Annual reports (CCR): links to utility Consumer Confidence Reports are hand-curated for large systems and verified to return HTTP 200 before publishing. Missing links mean we have not yet confirmed a stable public URL.