California Water Service - San Mateo
PWSID: CA4110008
This system has no unresolved violations. The most recent violation on record was 1992-10-01.
System Details
| Population Served | 102,348 |
| Service Connections | 25,440 |
| Water Source | Surface Water Purchased |
| System Type | Community Water System |
| Owner | Private |
| Status | Active |
| City | San Jose |
| EPA ZIP on File | 95112 |
Lead & Copper Testing
| Contaminant | Level | EPA Action Level | Status |
|---|---|---|---|
| Lead (90th percentile) | 0.0059 mg/L | 0.015 mg/L | Below Action Level |
| Lead (90th percentile) | 0.0046 mg/L | 0.015 mg/L | Below Action Level |
| Lead (90th percentile) | 0.0044 mg/L | 0.015 mg/L | Below Action Level |
| Lead (90th percentile) | 0.0000 mg/L | 0.015 mg/L | Below Action Level |
Violation History (2 total)
| Contaminant | Violation | Date | Health-Based | Status |
|---|---|---|---|---|
| 3100 | MCL | 1992-10-01 | Yes | Returned to Compliance |
| 3100 | MCL | 1992-10-01 | Yes | Returned to Compliance |
Understanding This Water System's Record
California Water Service - San Mateo is a community water system water system that draws from surface water purchased sources and serves a population of 102,348 in San Jose, California. This page shows its complete compliance history as reported to the EPA's Safe Drinking Water Information System (SDWIS), the federal database that tracks every public water system in the United States.
What Do These Violations Mean?
Health-based violations mean the system exceeded an EPA maximum contaminant level (MCL) or failed to provide required treatment. These indicate potential health risks from contaminants like lead, arsenic, bacteria, nitrates, or disinfection byproducts. Non-health-based violations involve monitoring, reporting, or procedural requirements — the system missed a testing deadline or failed to notify customers, but contaminant levels were not necessarily unsafe.
What Should You Do?
Your water utility is required to publish an annual Consumer Confidence Report (CCR) that details test results and any violations. If your system has active health-based violations, consider a certified water filter rated for the specific contaminants involved. The contaminant guides on this site explain health risks and filter options for common pollutants. For the most current results, contact your water utility directly — EPA data can lag weeks or months behind real-time testing.