State profile · EPA SDWIS + UCMR5
EPA Region 9 — Tribal Water Systems Drinking Water Quality
323 SDWIS-listed public water systems serve 555,721 people across EPA Region 9 — Tribal Water Systems. Violation rates use that full inventory; PFAS rates use only the UCMR5-tested subset.
- 323
- SDWIS water systems
- 48,296
- Total violations
- 96.6%
- SDWIS systems w/ a violation
- 19.5%
- UCMR5 PFAS rate (41 tested)
The verdict
555,721 people served via SDWIS-listed systems - smaller served population (≤ 1,083,630). According to EPA SDWIS population served, EPA Region 9 — Tribal Water Systems ranks #53 of 66 states and territories by people served through public water systems.
- #53 of 66
- Population · states corpus
- 48,296
- Total EPA violations on record
- 7%
- Health-based (MCL / treatment)
- 96.6%
- SDWIS systems with ≥1 violation
SDWIS violation % and UCMR5 PFAS % use different denominators (full inventory vs tested subset). Population ordinal uses SDWIS population served.
EPA Region 9 — Tribal Water Systems standing, high SDWIS violation-rate third
EPA Region 9 — Tribal Water Systems sits in the upper third of jurisdictions by SDWIS violation rate (96.6%), so the system lists below sample one of the denser state-level compliance trails in this extract. Population served is smaller (555,721; smaller served population (≤ 1,083,630)), so a high rate can still mean a compact household footprint. Health-based share is only 7% - almost all of this trail is monitoring/reporting rather than MCL exceedance. UCMR5 PFAS detection is 19.5% on the tested subset (mid UCMR5 detection (≤ 35.3%)) - a different denominator from the SDWIS violation rate. Systems listed below are ranked by population served or violation count; pair rate with inventory size before reading exposure scale.
Nationwide similar states
Nearest by SDWIS violation rate
Nearest by population served
Health-based share of this violation record
EPA SDWIS classifications for EPA Region 9 — Tribal Water Systems's 48,296 recorded violations.
EPA Region 9 — Tribal Water Systems vs nearest violation-rate peers
Share of SDWIS-listed systems with at least one recorded violation; peers are nearest by absolute rate distance, not a fixed top-seven list.
- 09
EPA Region 9 — Tribal Water Systems
96.6 % of systems
- 08
EPA Region 8 — Tribal Water Systems
96.3 % of systems
- NM
New Mexico
96.9 % of systems
- ID
Idaho
96.1 % of systems
- MS
Mississippi
96.1 % of systems
What this shows EPA Region 9 — Tribal Water Systems's rate is 96.6% (312 of 323 systems; upper-third rate (> 96.1%)). This is a comparison of recorded SDWIS violations, not a measure of current water safety.
EPA Region 9 — Tribal Water Systems vs all jurisdictions by SDWIS system inventory
Where this state's public water system count sits among every state and territory on PlainWater
323 51st of 66 higher than 15 of 66 jurisdictions
States and territories, banded by SDWIS-listed public water system count
Each bar is a band; taller bars hold more jurisdictions. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count and share, and where it sits relative to this entry.
Source EPA SDWIS state aggregates · 2026-05-15
Largest Water Systems
Most Violations
Counties in EPA Region 9 — Tribal Water Systems
Showing top 30 of 31 counties.
Context: Check your water system · methodology · all states
Every figure on PlainWater is rendered directly from EPA SDWIS drinking-water data, no number is typed in by an editor. This page draws directly on EPA SDWIS data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.