PlainWater

St. Louis County, Missouri

SDWIS compliance plate

Sheet MO189 · St. Louis County 23 sys · 1,825 viol · #45/3254

VIOL-SEVERE · HEALTH-MID · RANK-TOP · PHOTO-FINISH · PFAS-HIGH · SRC-GW · SYS-SMALL · BOOK-FULL

  • VIOL-SEVERE 95.7% flagged
  • HEALTH-MID 20.0% health
  • RANK-TOP #45/3254
  • PHOTO-FINISH ±0.0 pp
  • PFAS-HIGH 50.0% detect
  • SRC-GW GW lead 87%
  • SYS-SMALL 23 systems
  • BOOK-FULL 7/7 fields

Nearest flagged-rate peer: Iron County (+ 0 pp flagged-rate)

According to EPA SDWIS county population served used on /counties, St. Louis County ranks #45 of 3,254 counties by people served, and #1 of 115 counties in Missouri. See methodology · corpus placement.

St. Louis County standing, mid-flagged corpus third

Flagged-system rate 95.7% is in the corpus middle third (≤ 100.0% flagged) across 2,973 counties with ≥3 SDWIS systems . Health-based share 20.0% is health-based share in the middle third (≤ 24.5%) . UCMR5 detect rate 50.0% is UCMR5 detect rate above the tested-pool upper third (> 33.3%) . Population served ranks #45 of 3,254 · #1 of 115 in Missouri.

Flagged-rate neighbourhood around St. Louis County

Lowest/highest poles plus in-state counties nearest St. Louis County on % of SDWIS systems with ≥1 violation. Full ladder: /counties.

0% 20% 40% 60% 80% 100% Shannon · lowest Montgomery · near Iron · near Mercer · highest 69.6% 95.5% 95.5% 95.7% 95.7% 95.7% 100%

Source: EPA SDWIS (county aggregates) As of 2026-05-15

Water Systems

Compare beyond Missouri

Mid-flagged peers for St. Louis County

Cross-state counties nearest St. Louis County on flagged-system share (95.7%) and cumulative violation count (1,825). In-state neighbours stay on the compliance plate above.

Similar flagged-system rate

Nearest cross-state counties by % of SDWIS systems with at least one violation on record.

4 peers

Similar violation load

Nearest cross-state counties by cumulative SDWIS violation count (all systems in the county).

4 peers
Data sourced from EPA SDWIS and UCMR5 PFAS monitoring data. See our methodology for details. Retrieved and formatted by PlainWater

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.