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Drinking water tools

Compare counties side by side on EPA Safe Drinking Water Act violations and UCMR5 PFAS testing, or open high-violation counties from the national inventory.

143,076
Public water systems
88.4%
Systems with ≥1 violation
34.4%
UCMR5 PFAS detection rate

According to the U.S. Environmental Protection Agency Safe Drinking Water Information System (SDWIS) and UCMR5 testing program (data vintage 2026-05-15), every figure on this page is drawn from official public water-system records. See our methodology for how violations and PFAS detections are counted.

What these tools answer

EPA SDWIS tracks 143,076 public water systems; 88.4% carry at least one recorded violation, and 34.4% of UCMR5-tested systems show PFAS. Use the county compare tool to put any two counties side by side on the same official metrics.

143,076
Public water systems tracked
88.4%
Systems with ≥1 SDWIS violation
34.4%
UCMR5 PFAS detection rate
3,254
Counties available to compare

Compare uses county aggregates from the same SDWIS and UCMR5 extracts as system and state pages. See methodology.

What a system lookup returns

Share of the 143,076 public water systems carrying each independently checkable layer. Base SDWIS record is always 100%; UCMR5 PFAS testing is a targeted, not universal, sampling program.

of systems

What this shows Every system has a base SDWIS record and population served. UCMR5 PFAS testing reached a much smaller, targeted share of systems, so a lookup returns a PFAS result only when that system was actually tested.

Source EPA SDWIS + UCMR5 water_systems extract As of 2026-05-15

County compare

Side-by-side water quality

Pick any two U.S. counties and compare violations, PFAS detection, and systems covered from EPA records.

State compare

State vs state rankings

Compare violation rates, PFAS UCMR5 detection, and system counts for any two states from SDWIS aggregates.

System lookup

Find a water system

Search by system name, city, or ZIP, then open the EPA violation and PFAS record for that public water system.

Popular county comparisons

Large counties by population served; open a ready-made pair in the compare tool.

Counties with the most recorded violations

Named counties with at least 20 water systems, ranked by total EPA SDWIS violations on record.

  1. 1. Orange County 85,938 violations
  2. 2. Harris County 78,495 violations
  3. 3. Monroe County 72,365 violations
  4. 4. Bucks County 59,577 violations
  5. 5. Berks County 54,767 violations
  6. 6. Lubbock County 50,449 violations

Download the SDWIS/UCMR5 state landscape snapshot cited on this page: sdwis-state-landscape.csv (same CSV as /statistics, CC0).

Every figure on PlainWater is rendered directly from EPA SDWIS drinking-water data, no number is typed in by an editor. Tool metrics on this page are computed from EPA SDWIS and UCMR5 extracts; no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2026-05-15.