States › Missouri › St. Charles County

St. Charles County, MO Water Quality

Water quality data for 8 public water systems serving St. Charles County, Missouri — based on EPA SDWIS enforcement records, lead testing results, and health-based violation history.

📅 2026 Report 🔄 Data updated 2026 Q2 📍 8 water systems · 17 cities
✅
Excellent — All Systems Performing Well

Water quality across the county is outstanding with minimal violations and very low lead levels.

A

St. Charles County Earns a A

St. Charles County: 17 communities across 8 water systems. 100.0% have no open violations.

  • Median lead where detected: 3.69 ppb
  • 4 communities with a lead detection, 13 reporting none detected
  • 1 communities with PFAS above the federal limit
  • 11 with significant inspection deficiencies
  • 100.0% of communities have no open violations
3.69 ppb
Median Lead Level
County-wide, 90th percentile
8
Water Systems
Active CWS & NTNCWS
100%
Violation-Free
No active violations on record
How we grade counties: MyWaterIQ uses EPA SDWIS enforcement data — actual MCL violations and lead test results — not the aspirational MCLG targets used by some sites. A grade reflects real compliance history, not theoretical risk. Learn more →

Cities by Water Quality

⭐ Best Performing
  • St. Charles
    Not detected
    No federal limits exceeded on record
    A
  • Weldon Spring
    Not detected
    No federal limits exceeded on record
    A
  • Cottleville
    Not detected
    No federal limits exceeded on record
    A
  • St. Paul
    Not detected
    No federal limits exceeded on record
    B
  • Flint Hill
    4.77 ppb
    No federal limits exceeded on record
    A
⚠ Needs Attention
  • St. Peters
    Not detected
    PFAS above the limit at 1 of 2 sampling points
    C
  • Portage Des Sioux
    2.60 ppb
    1 significant inspection deficiency
    B
  • O'Fallon
    Not detected
    2 significant inspection deficiencies
    A
  • Wentzville
    Not detected
    2 significant inspection deficiencies
    A
  • Lake St. Louis
    Not detected
    2 significant inspection deficiencies
    A
County Lead Level — Median 3.69 ppb
Based on most recent 90th percentile lead tests across all reporting systems
0 ppb5 ppb10 ppb15 ppb
County median: 3.69 ppb — 24.6% of the federal action level
Systems by Lead Level
Under 5 ppb
4
No Data
13

All Cities in St. Charles County

St. Charles Not detected A
O'Fallon Not detected A
St. Peters Not detected C
Wentzville Not detected A
Lake St. Louis Not detected A
Dardenne Prairie Not detected A
Weldon Spring Not detected A
Cottleville Not detected A
St. Paul Not detected B
New Melle Not detected A
Foristell 2.32 ppb B
Flint Hill 4.77 ppb A
Portage Des Sioux 2.60 ppb B
Josephville 4.77 ppb A
Defiance Not detected A
Augusta Not detected A
Weldon Spring Heights Not detected A
Showing 17 cities
No active violations Active violations

About St. Charles County Drinking Water

St. Charles County is served by 8 water systems covering 17 communities. No community here has an open violation on record.

Of the communities reporting lead results, 4 recorded a detection, with a median of 3.69 ppb — 25% of the federal action level. 13 reported none detected, which means below the laboratory limit rather than an absence of lead.

1 of 17 communities have PFAS above the limits EPA set in 2024, measured as a running annual average at each sampling point. State inspectors recorded significant deficiencies at 11 of them.

Frequently Asked Questions

Is St. Charles County tap water safe to drink?▼
No community in St. Charles County has an open violation on record. 1 of 17 have PFAS above the federal limit, which is the main open concern.
What is the lead level in St. Charles County?▼
Among communities with a detection the median is 3.69 ppb, 25% of the 15 ppb action level. 13 reported none detected and 0 reported no result.
How many water systems serve St. Charles County?▼
8 community water systems serve 17 communities here.
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