California Water Service - San Mateo
EPA ID: CA4110008 · 102,348 people served · 4 ZIP codes
ZipCheckup's reading of EPA SDWIS for California Water Service - San Mateo (CA4110008): no EPA violations recorded in the last five years. Although compliance varies widely among water utilities nationally, California Water Service - San Mateo stands out with zero EPA violations over five consecutive monitoring years, delivering safe tap water to 102,348 residents and showing no enforcement activity across the entire reporting span.
Data: EPA SDWIS
Service Area Map
Coverage area for California Water Service - San Mateo Source: EPA SDWIS service area boundaries.
Service area boundary
Service Area Demographics
The California Water Service - San Mateo serves a community with a median household income of $179,754 and an estimated 140,535 residents across its service area. 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
Estimated Remediation Costs
Average estimated costs across ZIP codes served by this system
Based on national averages for common remediation projects. Actual costs vary by property. Only issues flagged by EPA, FEMA, or state data for each ZIP code are included.
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: Let cold water run for 2 minutes before drinking — this helps flush lead from your pipes.
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 the full compliance record 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: Tested Clean
This water system was tested under the federal EPA Unregulated Contaminant Monitoring Rule (UCMR5). No PFAS compounds were detected.
Current MCL reflects the lowest state-enforceable limit (NYS 10 ppt for PFOA/PFOS, effective August 2020). The federal final MCL of 4 ppt for PFOA/PFOS (EPA April 2024 rule) is not enforceable until April 2029. Detections above 4 ppt but below 10 ppt are below current MCL but above the future federal limit.
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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