Every data source behind the $15 brief, every formula we use to derive a metric, every assumption we make when a ZIP straddles two utilities. If a number isn't sourced, it isn't in the report.
The order form takes a 5-digit US ZIP code. We resolve ZIP → PWS (Public Water System) through the EPA's Safe Drinking Water Information System (SDWIS) and state PWS service-area boundaries, where published. A ZIP that maps to multiple PWSs returns the largest by population served unless the user has named their utility on the order form, in which case the named utility takes precedence. A ZIP that does not resolve to a covered PWS triggers an automatic refund.
Every brief is compared against the federal Maximum Contaminant Levels finalised in 40 CFR § 141.61(c) and published at 89 Fed. Reg. 32532 (April 26, 2024). The thresholds are:
The Hazard Index is calculated as the sum of (measured concentration ÷ health-based water concentration) for each of the four mixture components. The brief shows the computed HI value alongside the per-compound results.
Where a state has adopted an enforceable PFAS MCL stricter than the federal floor on any compound or covering a compound not in the federal rule, the brief uses the stricter state value. Currently this affects briefs for utilities in Michigan (MPART rule R 325.10604g), New Jersey (DEP), New Hampshire (DES under RSA 485:16-e), Massachusetts (DEP sum-of-6), and New York (DOH). See the state regulation guide for the per-state limits used.
The occurrence data underlying each brief is the EPA Fifth Unregulated Contaminant Monitoring Rule (UCMR 5) public dataset, published quarterly to the EPA National Contaminant Occurrence Database (NCOD) at ncod.epa.gov. UCMR 5 covers 29 PFAS analytes plus lithium and was promulgated at 87 Fed. Reg. 80415 (December 27, 2022). Sampling runs 2023–2025; analyses follow EPA Method 537.1 (long-chain) and Method 533 (short-chain).
Where a utility's UCMR 5 sampling has not yet completed, the brief uses the most recent prior data available (state-DEP files, voluntary utility disclosures, UCMR 3 if relevant) and marks the result as "interim" with the source year.
The "state detection rate" cell on the brief is the share of UCMR 5 sampled PWSs in the user's state that returned at least one PFAS detection above the Minimum Reporting Level (MRL). The "median total PFAS" is the median sum of all detected PFAS across detecting utilities in that state.
Both values are recomputed each quarter as new UCMR 5 data is published. Briefs are dated to the EPA NCOD release used.
A utility is tagged "HOTSPOT" when at least one of these is true: (a) any UCMR 5 or state-DEP PFAS detection above 10 ng/L for any single compound; (b) the utility is within a documented PFAS plume named in a consent order, ATSDR exposure assessment, or DoD AFFF site inventory; (c) the utility is downstream of a known PFAS-manufacturing source (Chemours Fayetteville, 3M Decatur, etc.). Tier categories are LOW · ELEVATED · HOTSPOT. The criteria for each are listed on the brief's footnote line.
Filter recommendations are by certification category, not by brand. The logic is:
Prices in the brief are pulled from each manufacturer's published 2026 list price and refreshed quarterly. We do not accept manufacturer placement payments.
When the order form's "Pregnancy or infant in the household" box is checked, the brief inserts an additional page citing the EFSA 2020 Tolerable Weekly Intake (4.4 ng/kg body weight/week for the sum of PFOA + PFOS + PFNA + PFHxS; EFSA Journal 2020;18(9):6223) and the ATSDR Clinician's Guide on PFAS. The callout is educational and explicitly directs the reader to consult their obstetrician or pediatrician. See the pregnancy guide for the underlying logic.
Lab recommendations require: EPA Method 537.1 OR 533 (preferably both run in combination), and NELAP accreditation. Three labs currently meeting both criteria with consumer mail-in kits are named in the brief without endorsement, see the testing guide.
The current data snapshot powering briefs is the EPA NCOD release of June 2026. The next scheduled refresh is the September 2026 NCOD quarterly publication. Each brief is dated to the snapshot it used.
