Data Sources
Transparency is core to what we do. Every WaterVerge grade is derived from publicly available federal datasets — here is exactly where the data comes from.
Primary Data Sources
WaterVerge grades are built from three core EPA datasets. Each provides a different lens on drinking water quality — violations and enforcement, PFAS contamination, and lead exposure risk.
EPA SDWIS
Safe Drinking Water Information System
The backbone of every WaterVerge grade. SDWIS contains violation records, water system registrations, enforcement actions, and compliance history for all 150,000+ public water systems in the United States.
EPA UCMR 5
Unregulated Contaminant Monitoring Rule, 5th Cycle
The first nationwide testing program for PFAS in drinking water. UCMR 5 covers 29 PFAS compounds — including PFOA, PFOS, and 27 others — across thousands of water systems sampled between 2023 and 2025.
EPA Envirofacts LCR
Lead and Copper Rule via Envirofacts API
90th percentile lead and copper testing results from routine sampling required under the EPA's Lead and Copper Rule. These results indicate whether a water system's distribution infrastructure may be contributing lead or copper to tap water.
State Environmental Agencies
Federal EPA data provides the foundation for every grade, but some states maintain their own compliance databases that offer additional detail or more current records. Where available, we cross-reference state-level data to supplement the federal picture.
State-level cross-referencing
Many state environmental and health departments operate independent compliance databases that track violations, sampling results, and enforcement actions. These databases sometimes contain records not yet reflected in EPA SDWIS, or provide more granular detail on local issues.
Filling the gaps
When state-level data provides more recent or detailed records for a water system, we incorporate it to ensure grades reflect the most complete picture available. Federal EPA data always serves as the baseline — state data supplements but never overrides it.
Ongoing expansion
We are continuously expanding state-level integration. If your state environmental agency publishes drinking water compliance data and you believe it should be reflected in WaterVerge grades, we welcome the feedback.
Data Freshness
We refresh our data on a regular cadence to match EPA publication schedules. Every grade you see on WaterVerge reflects the most recent data available at the time of our last refresh.
We re-import and recompute all grades each quarter, aligned with EPA's SDWIS publication schedule. UCMR 5 data is incorporated whenever EPA publishes new batches (typically 2–3 times per year).
All WaterVerge grades currently reflect data imported and scored during this refresh cycle. The date of the last refresh is also shown on individual city pages.
Our pipeline downloads raw EPA data, normalizes records, maps systems to cities and ZIP codes, computes subscores, and generates the final letter grade — all programmatically with manual QA checks.
Data Limitations
No dataset is perfect. We believe in being upfront about what our grades can and cannot tell you. Understanding these limitations is important for interpreting WaterVerge scores correctly.
Community water systems only
WaterVerge grades cover public community water systems (CWS) as defined by EPA. Private wells, which serve approximately 43 million Americans, are not monitored by EPA and are not included in our data. If your home uses a private well, your water quality is not reflected here.
EPA reporting timelines
There is an inherent lag between when a violation occurs and when it appears in EPA databases. States report to EPA on varying schedules, and some violations may take weeks or months to be reflected in SDWIS. Our grades are only as current as the underlying EPA data.
Small system data gaps
Some small water systems (serving fewer than 500 people) may have incomplete violation or sampling records in federal databases. Where data is limited, our grade capping system prevents artificially high scores — but the grade may not fully reflect actual water quality.
PFAS coverage is evolving
UCMR 5 is the first nationwide PFAS monitoring program, and not every water system has been tested yet. Cities without UCMR 5 data receive a slight score penalty for unknown PFAS status rather than a perfect subscore. As more data is published, coverage will improve.
Want to understand how we turn this data into grades?
Our methodology page explains the full scoring formula — violation weights, PFAS thresholds, lead deductions, and grade capping rules.