California Water Service - San Mateo
EPA ID: CA4110008 · 102,348 people served · 4 ZIP codes
ZipCheckup's reading of EPA records for California Water Service - San Mateo (CA4110008): no drinking-water violations recorded since 2021. Although compliance varies widely among water utilities nationally, the SDWIS file for California Water Service - San Mateo lists no EPA violations for this supplier, whose service area covers 102,348 residents.
Data: EPA SDWIS
Service Area Map
Coverage area for California Water Service - San Mateo Source: EPA SDWIS service area boundaries.
Service area boundary
Demographics of ZIP Codes Served
The ZIP codes associated with California Water Service - San Mateo have a median household income of $179,754 and about 140,535 residents live in those ZIP codes (Census; not the number of people this system supplies). Approximately 79% of housing stock was built before 1986, which increases the likelihood of lead service lines and older plumbing.
🌊 Where Does Your Water Come From?
California Water Service - San Mateo's water is drawn from rivers, lakes, or reservoirs. Surface water sources are more exposed to agricultural runoff, stormwater, and upstream discharges, but they typically receive more intensive treatment before reaching your tap.
Superfund Proximity Note: This service area ranks in the 60th percentile nationally for proximity to Superfund (NPL) sites.
Infrastructure Risk
Comparable Water Systems
Similar-sized systems in California
System Overview
California Water Service - San Mateo (EPA ID: CA4110008) is a community water system in California that serves approximately 102,348 people from surface water sources.
This system provides water to 4 ZIP codes across 1 community.
Violation History
Lead & Copper
EPA Lead and Copper Rule evidence attributed directly to this water system:
| Lead Level | Exceeds Action Level | Sample Date |
|---|---|---|
| 0.0044 mg/L | No | N/A |
No copper action-level exceedance record appears for this PWSID in the accepted LCR snapshot. This does not establish a clean copper measurement.
Radon Risk in Service Area
Dominant radon zone for ZIP codes served by this system: Zone 2 (Moderate Risk)
The EPA recommends testing homes in Zone 1 and Zone 2 areas for radon.
Need help with your water quality?
Typical cost: Water test: typically $20–$50 (DIY kit) · Professional inspection: $150–$400
Find the Right Water FilterFree tip: Ask your water utility whether running cold water for 2 minutes is enough to flush your plumbing before drinking.
ZIP Codes Served
Coverage: Service area ZIP codes sourced from EPA Community Water System Service Area Boundaries v3 (March 2026 release). These ZIPs reflect the actual deployment footprint recorded by CA or modeled from parcel and building-footprint data.
Data Sources
This report uses public data from the EPA Safe Drinking Water Information System (SDWIS). View available EPA compliance records for California Water Service - San Mateo (CA4110008) on EPA.gov.
Frequently Asked Questions
Is California Water Service - San Mateo water safe to drink?
The accepted 2026Q2 ECHO snapshot contains zero violation records for California Water Service - San Mateo in the inclusive 2021-2026 record-year window. This is a compliance-record finding, not a guarantee about water at a specific tap.
How many people does California Water Service - San Mateo serve?
California Water Service - San Mateo serves approximately 102,348 people across 4 ZIP codes in California.
Where does California Water Service - San Mateo get its water?
The primary water source is surface water.
Federal UCMR5 PFAS Monitoring: No PFAS Reported Above Reporting Levels
This water system was tested under the federal EPA Unregulated Contaminant Monitoring Rule (UCMR5). No PFAS compounds were reported above UCMR5 minimum reporting levels.
EPA's April 2024 PFAS rule sets MCLs of 4 ppt for PFOA and PFOS and 10 ppt for PFHxS, PFNA and HFPO-DA (GenX); water systems must comply from 2029. Other PFAS compounds have no individual federal MCL. A state standard is shown only where this system's state has its own enforceable PFAS limit. Detection results are EPA UCMR5 samples, not a measurement at your tap.
Source: U.S. EPA UCMR5 (Unregulated Contaminant Monitoring Rule, 5th cycle) — per-system federal sampling, 2023–2025. EPA UCMR5 monitoring program →
Frequently Asked Questions
How to cite this page
ZipCheckup. (n.d.). California Water Service - San Mateo, CA: Serves 102K People. https://zipcheckup.com/water-system/ca4110008/
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