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Jefferson County, WI Water Quality

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

📅 2026 Report 🔄 Data updated 2026 Q2 📍 12 water systems · 20 cities
✅
Generally Safe — Most Systems Performing Well

The majority of water systems have no active violations and lead levels well below the federal action level.

B

Jefferson County Earns a B

Jefferson County: 20 communities across 12 water systems. 100.0% have no open violations.

  • Median lead where detected: 3.80 ppb
  • 20 communities with a lead detection, 0 reporting none detected
  • 2 communities with PFAS above the federal limit
  • 5 with significant inspection deficiencies
  • 100.0% of communities have no open violations
3.8 ppb
Median Lead Level
County-wide, 90th percentile
12
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
  • Concord
    0.49 ppb
    No federal limits exceeded on record
    B
  • Watertown
    11.00 ppb
    Lead at 11.00 ppb, above a third of the action level
    A
  • Watertown
    11.00 ppb
    Lead at 11.00 ppb, above a third of the action level
    A
  • Cold Spring
    10.00 ppb
    Lead at 10.00 ppb, above a third of the action level
    A
  • Ixonia
    0.83 ppb
    Copper above the 1,300 ppb action level
    B
⚠ Needs Attention
  • Lake Mills
    4.60 ppb
    Copper above the 1,300 ppb action level
    C
  • Johnson Creek
    2.80 ppb
    3 significant inspection deficiencies
    C
  • Aztalan
    4.60 ppb
    Copper above the 1,300 ppb action level
    C
  • Lake Mills
    4.60 ppb
    Copper above the 1,300 ppb action level
    C
  • Farmington
    2.80 ppb
    3 significant inspection deficiencies
    C
County Lead Level — Median 3.8 ppb
Based on most recent 90th percentile lead tests across all reporting systems
0 ppb5 ppb10 ppb15 ppb
County median: 3.8 ppb — 25.3% of the federal action level
Systems by Lead Level
Under 5 ppb
15
10 – 15 ppb
5

All Cities in Jefferson County

Watertown 11.00 ppb A
Fort Atkinson 13.00 ppb B
Jefferson 3.50 ppb B
Lake Mills 4.60 ppb C
Waterloo 1.30 ppb B
Johnson Creek 2.80 ppb C
Palmyra 3.80 ppb B
Ixonia 0.83 ppb B
Koshkonong 13.00 ppb B
Sullivan 0.19 ppb B
Oakland 1.68 ppb B
Concord 0.49 ppb B
Aztalan 4.60 ppb C
Watertown 11.00 ppb A
Lake Mills 4.60 ppb C
Jefferson 3.50 ppb B
Cold Spring 10.00 ppb A
Palmyra 3.80 ppb B
Farmington 2.80 ppb C
Milford 4.60 ppb C
Showing 20 cities
No active violations Active violations

About Jefferson County Drinking Water

Jefferson County is served by 12 water systems covering 20 communities. No community here has an open violation on record.

Of the communities reporting lead results, 20 recorded a detection, with a median of 3.80 ppb — 25% of the federal action level. 0 reported none detected, which means below the laboratory limit rather than an absence of lead.

2 of 20 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 5 of them.

Frequently Asked Questions

Is Jefferson County tap water safe to drink?▼
No community in Jefferson County has an open violation on record. 2 of 20 have PFAS above the federal limit, which is the main open concern.
What is the lead level in Jefferson County?▼
Among communities with a detection the median is 3.80 ppb, 25% of the 15 ppb action level. 0 reported none detected and 0 reported no result.
How many water systems serve Jefferson County?▼
12 community water systems serve 20 communities here.
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