Is San Mateo, California tap water safe?
2 water systems report serving San Mateo. Your water depends on which one serves your address. Check your bill if unsure. This list is matched from the ZIP codes in this place, so it may include nearby systems.
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California Water Service - San Mateo
Serves 103,536 people · Surface water · Full report →
No health-based violations in the last 5 years; PFAS tested (UCMR 5), none above federal limits; Lead 90th percentile below the action level (2025).
A
Estero Municipal Improvement District
Serves 36,556 people · Surface water · Full report →
No health-based violations in the last 5 years; 1 monitoring/reporting violation; PFAS tested (UCMR 5), none above federal limits; Lead 90th percentile below the action level (2025).