States › California › San Mateo County

San Mateo County, CA Water Quality

Water quality data for 19 public water systems serving San Mateo County, California — based on EPA SDWIS enforcement records, lead testing results, and health-based violation history.

📅 2026 Report 🔄 Data updated 2026 Q2 📍 19 water systems · 33 cities
✅
Excellent — All Systems Performing Well

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

A

San Mateo County Earns a A

San Mateo County: 33 communities across 19 water systems. 100.0% have no open violations.

  • Median lead where detected: 4.00 ppb
  • 20 communities with a lead detection, 13 reporting none detected
  • 0 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
19
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
  • Daly City
    Not detected
    No federal limits exceeded on record
    A
  • San Mateo
    4.40 ppb
    No federal limits exceeded on record
    A
  • South San Francisco
    4.10 ppb
    No federal limits exceeded on record
    A
  • San Bruno
    Not detected
    No federal limits exceeded on record
    A
  • Pacifica
    Not detected
    No federal limits exceeded on record
    A
⚠ Needs Attention
  • Pescadero
    0.60 ppb
    Copper above the 1,300 ppb action level
    B
  • San Carlos
    5.80 ppb
    1 health-based violation since 2015
    B
  • Moss Beach
    Not detected
    Copper above the 1,300 ppb action level
    A
  • Montara
    Not detected
    Copper above the 1,300 ppb action level
    A
  • Burlingame
    6.30 ppb
    Lead at 6.30 ppb, above a third of the action level
    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
18
5 – 10 ppb
2
No Data
13

All Cities in San Mateo County

Daly City Not detected A
San Mateo 4.40 ppb A
Redwood City Not detected B
South San Francisco 4.10 ppb A
San Bruno Not detected A
Pacifica Not detected A
Foster City Not detected A
Burlingame 6.30 ppb B
San Carlos 5.80 ppb B
Belmont Not detected A
East Palo Alto Not detected B
Millbrae Not detected A
Menlo Park 4.00 ppb A
North Fair Oaks 4.00 ppb A
Half Moon Bay 1.60 ppb A
Hillsborough Not detected A
Atherton 4.00 ppb A
El Granada 1.60 ppb A
Woodside 4.00 ppb A
Portola Valley 4.00 ppb A
Emerald Lake Hills Not detected B
Broadmoor 4.10 ppb A
West Menlo Park 4.00 ppb A
Brisbane 3.00 ppb B
Moss Beach Not detected A
Montara Not detected A
Highlands 4.40 ppb A
Baywood Park 4.40 ppb A
Ladera 4.00 ppb A
Colma 4.10 ppb A
La Honda 4.00 ppb A
Pescadero 0.60 ppb B
Loma Mar Not detected B
Showing 33 cities
No active violations Active violations

About San Mateo County Drinking Water

San Mateo County is served by 19 water systems covering 33 communities. No community here has an open violation on record.

Of the communities reporting lead results, 20 recorded a detection, with a median of 4.00 ppb — 27% of the federal action level. 13 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 San Mateo County tap water safe to drink?▼
No community in San Mateo County has an open violation on record. No community has PFAS above the federal limit on record.
What is the lead level in San Mateo County?▼
Among communities with a detection the median is 4.00 ppb, 27% of the 15 ppb action level. 13 reported none detected and 0 reported no result.
How many water systems serve San Mateo County?▼
19 community water systems serve 33 communities here.
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