EPA SDWIS + UCMR5 · 2026-05-15
Drinking water statistics
Registry counts from this PlainWater extract of EPA SDWIS and UCMR5. 143,076 public water systems, 66 states and territories. Not tap-water advice and not a safety ranking.
- 143,076
- Public water systems
- 1,262,223
- Contaminant-summary rows
- 10,252 tested
- UCMR5 PFAS systems
- 34.4%
- PFAS detection among tested
This extract · 2026-05-15
This SDWIS inventory holds 143,076 public water systems. 88.4% carry at least one recorded violation. 34.4% of 10,252 UCMR5-tested systems show a PFAS detection.
- 143,076
- Public water systems
- 88.4%
- Systems with a recorded violation
- 1,262,223
- System-contaminant summary rows
- 34.4%
- PFAS detection among tested
According to this PlainWater extract of EPA SDWIS and UCMR5. See methodology. Figures recompute from the live tables.
According to this PlainWater extract (data vintage 2026-05-15), 143,076 public water systems appear in EPA SDWIS. Read the methodology.
Key findings
Standalone, citable statements from this extract. This derived page is CC0.
- 143,076 public water systems sit in this SDWIS inventory (CWS, NTNCWS, and TNCWS). Counts recompute from water_systems, not a typed census.
- 66 / 3,254 / 157 states and territories / counties / contaminant codes appear in this extract. County rows include 88 EPA-region tribal groupings that the sitemap withholds.
- 126,455 of 143,076 systems (88.4%) carry at least one recorded SDWIS violation in this extract. That is a recorded-violation share, not a share of unsafe taps.
- 1,262,223 system-contaminant rows sit in violations_summary. Summed violation_count is 9,922,446. That grain is not SUM(water_systems.total_violations) = 10,559,500.
- Coliform (TCR) is the largest contaminant category in violations_summary (1,839,196 of 9,922,446 summed violation_count). Category share is a recording mix, not a toxicity rank.
- 3,528 of 10,252 UCMR5-tested systems show a PFAS detection (34.4% of tested systems, not of all 143,076). The panel has 29 compounds and 1,863,306 occurrence rows.
- 10,988 Wisconsin holds 10,988 of 143,076 systems (7.7%); Michigan holds 10,959. Inventory share is small-system grain, not a water-quality rank.
- 1,159,868 recorded SDWIS violation events sit on Pennsylvania systems, the largest state total in this extract. Event volume is not a safety ranking. Health-based flags are 1,513,732 of 10,559,500 rolled-up events (14.3%).
Where systems sit in this inventory
Top states by public-water-system count. Wisconsin and Michigan lead because they file many small systems, not because the water is worse.
Source: U.S. Environmental Protection Agency SDWIS Federal Reporting Services and UCMR5 occurrence · 2026 Inventory counts and recorded-violation totals describe this extract. They are not tap-water safety scores.
How to read these numbers
SDWIS violation events, health-based flags, and UCMR5 detections are federal reporting fields. A high event total can mean more systems, more reporting, or more recorded non-compliance - not a ranked "worst water" list. UCMR5 coverage is a tested subset. Download the state landscape CSV or open a state page.
Download the SDWIS/UCMR5 state landscape snapshot cited on this page: sdwis-state-landscape.csv (same CSV as /statistics, CC0).
License: CC0 1.0 for this derived Key Findings page and CSV.
Every figure on PlainWater is rendered directly from EPA SDWIS drinking-water data, no number is typed in by an editor. This page's Key Findings are aggregates over water_systems, violations_summary, states, and pfas_results in the live SQLite extract. Same tables as system, state, and county pages. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2026-05-15.