Methodology: How PurityMap Analyzes Water
How we turn public EPA and utility records into a reproducible, per-contaminant Purity Score.
Where the numbers come from
Every finding is drawn from a published record: EPA SDWIS compliance monitoring, the fifth Unregulated Contaminant Monitoring Rule (UCMR5) for PFAS, and utilities’ own Consumer Confidence Reports. We do not generate measurements; each one links back to its dated source.
The Purity Score
The Purity Score is computed only over contaminants that were actually measured, scored per-contaminant against health-based reference levels, then rolled up by category (PFAS, metals, disinfection by-products) into a 0–100 overall. The same inputs always produce the same score.
Score is separate from confidence
A score answers “how do the measured results look?” Confidence answers “how much was measured?” We report them separately, so a clean-but-thinly-tested system is never mistaken for a thoroughly-verified one.
Evidence gating
A contaminant that was never tested is shown as pending, never as a pass. A page or claim exists only when a dated measurement backs it. Absence of a measurement is not evidence of safety.
Limitations
Monitoring depth varies by system and year, and records can lag. These pages describe the public record for a system, not the water at your specific tap; confirm your supplier on your water bill and consider a certified home test for decisions.
PurityMap Editorial Team
This document is maintained by the PurityMap Editorial Team and updated with a visible modification date. See a discrepancy or have a question about this policy? Use the paths below.
Find the water system behind your tap
Start from an address, city or ZIP. Every report links to its public source.