States › New Jersey › Mercer County

Mercer County, NJ Water Quality

Water quality data for 7 public water systems serving Mercer County, New Jersey — based on EPA SDWIS enforcement records, lead testing results, and health-based violation history.

📅 2026 Report 🔄 Data updated 2026 Q2 📍 7 water systems · 12 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

Mercer County Earns a B

Mercer County: 12 communities across 7 water systems. 100.0% have no open violations.

  • Median lead where detected: 4.00 ppb
  • 10 communities with a lead detection, 2 reporting none detected
  • 3 communities with PFAS above the federal limit
  • 0 with significant inspection deficiencies
  • 100.0% of communities have no open violations
4 ppb
Median Lead Level
County-wide, 90th percentile
7
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
  • Hightstown
    1.70 ppb
    No federal limits exceeded on record
    A
  • Pennington
    1.00 ppb
    No federal limits exceeded on record
    B
  • East Windsor
    1.61 ppb
    1 health-based violation since 2015
    A
  • Hopewell
    Not detected
    2 health-based violations since 2015
    B
  • Princeton
    2.00 ppb
    PFAS above the limit at 3 of 7 sampling points
    B
⚠ Needs Attention
  • Robbinsville
    Not detected
    PFAS above the limit at 3 of 4 sampling points
    C
  • Trenton
    6.00 ppb
    20 health-based violations since 2015
    B
  • Hamilton
    6.00 ppb
    20 health-based violations since 2015
    B
  • Ewing
    6.00 ppb
    20 health-based violations since 2015
    B
  • Lawrence
    6.00 ppb
    20 health-based violations since 2015
    B
County Lead Level — Median 4 ppb
Based on most recent 90th percentile lead tests across all reporting systems
0 ppb5 ppb10 ppb15 ppb
County median: 4 ppb — 26.7% of the federal action level
Systems by Lead Level
Under 5 ppb
5
5 – 10 ppb
5
No Data
2

All Cities in Mercer County

Trenton 6.00 ppb B
Hamilton 6.00 ppb B
Ewing 6.00 ppb B
Princeton 2.00 ppb B
East Windsor 1.61 ppb A
West Windsor 2.00 ppb B
Lawrence 6.00 ppb B
Robbinsville Not detected C
Hopewell 6.00 ppb B
Hightstown 1.70 ppb A
Pennington 1.00 ppb B
Hopewell Not detected B
Showing 12 cities
No active violations Active violations

About Mercer County Drinking Water

Mercer County is served by 7 water systems covering 12 communities. No community here has an open violation on record.

Of the communities reporting lead results, 10 recorded a detection, with a median of 4.00 ppb — 27% of the federal action level. 2 reported none detected, which means below the laboratory limit rather than an absence of lead.

3 of 12 communities have PFAS above the limits EPA set in 2024, measured as a running annual average at each sampling point. State inspectors recorded no significant deficiencies.

Frequently Asked Questions

Is Mercer County tap water safe to drink?▼
No community in Mercer County has an open violation on record. 3 of 12 have PFAS above the federal limit, which is the main open concern.
What is the lead level in Mercer County?▼
Among communities with a detection the median is 4.00 ppb, 27% of the 15 ppb action level. 2 reported none detected and 0 reported no result.
How many water systems serve Mercer County?▼
7 community water systems serve 12 communities here.
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