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Tuolumne County, CA Water Quality

Water quality data for 12 public water systems serving Tuolumne County, California — based on EPA SDWIS enforcement records, lead testing results, and health-based violation history.

📅 2026 Report 🔄 Data updated 2026 Q2 📍 12 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

Tuolumne County Earns a A

Tuolumne County: 17 communities across 12 water systems. 82.4% have no open violations.

  • Median lead where detected: 4.70 ppb
  • 6 communities with a lead detection, 11 reporting none detected
  • 0 communities with PFAS above the federal limit
  • 0 with significant inspection deficiencies
  • 82.4% of communities have no open violations
4.7 ppb
Median Lead Level
County-wide, 90th percentile
12
Water Systems
Active CWS & NTNCWS
82%
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
  • Sonora
    Not detected
    No federal limits exceeded on record
    A
  • Jamestown
    Not detected
    No federal limits exceeded on record
    A
  • Columbia
    4.70 ppb
    No federal limits exceeded on record
    A
  • Tuolumne City
    Not detected
    No federal limits exceeded on record
    B
  • East Sonora
    Not detected
    No federal limits exceeded on record
    A
⚠ Needs Attention
  • Pine Mountain Lake
    Not detected
    1 violation currently open
    D
  • Groveland
    Not detected
    1 violation currently open
    D
  • Mono Vista
    Not detected
    1 violation currently open
    C
  • Long Barn
    Not detected
    Copper above the 1,300 ppb action level
    B
  • Mi-Wuk Village
    12.00 ppb
    Lead at 12.00 ppb, above a third of the action level
    B
County Lead Level — Median 4.7 ppb
Based on most recent 90th percentile lead tests across all reporting systems
0 ppb5 ppb10 ppb15 ppb
County median: 4.7 ppb — 31.3% of the federal action level
Systems by Lead Level
Under 5 ppb
4
10 – 15 ppb
2
No Data
11

All Cities in Tuolumne County

Sonora Not detected A
Jamestown Not detected A
Pine Mountain Lake Not detected D
Columbia 4.70 ppb A
Tuolumne City Not detected B
Mono Vista Not detected C
East Sonora Not detected A
Twain Harte Not detected B
Phoenix Lake Not detected B
Mi-Wuk Village 12.00 ppb B
Groveland Not detected D
Sierra Village 12.00 ppb B
Long Barn Not detected B
Cold Springs Not detected B
Tuttletown 4.70 ppb A
Strawberry 0.90 ppb B
Soulsbyville 4.00 ppb B
Showing 17 cities
No active violations Active violations

About Tuolumne County Drinking Water

Tuolumne County is served by 12 water systems covering 17 communities. 82% have no open violations.

Of the communities reporting lead results, 6 recorded a detection, with a median of 4.70 ppb — 31% of the federal action level. 11 reported none detected, which means below the laboratory limit rather than an absence of lead.

No community here has PFAS above the federal limit on record. State inspectors recorded no significant deficiencies.

Frequently Asked Questions

Is Tuolumne County tap water safe to drink?▼
82% of communities have no open violation. No community has PFAS above the federal limit on record.
What is the lead level in Tuolumne County?▼
Among communities with a detection the median is 4.70 ppb, 31% of the 15 ppb action level. 11 reported none detected and 0 reported no result.
How many water systems serve Tuolumne County?▼
12 community water systems serve 17 communities here.
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