County · California

San Mateo County, California: drinking water records

Name: Drinking water records for San Mateo County, California
Creator: U.S. Environmental Protection Agency
License: https://www.usa.gov/government-works

Explore EPA records for 36 community water systems across 30 ZIP codes in San Mateo County, then find water-testing resources and available recent monitoring-station readings.

In focus36Community water systems

Public records. Clearer context.

Data as of EPA UCMR 5 final release, August 2026 (file dated Aug 28, 2026) · EPA SDWIS 2026Q2 (file dated Jul 9, 2026). How we build these pages

Drinking-water records

EPA survey and compliance records are historical reports. UCMR 5 results are available for 19 of the 36 listed systems in this snapshot. A system with no reported PFAS detection is not a test of every tap or every contaminant.

systems in EPA's PFAS survey

systems where PFAS was found

systems at or above the PFOA or PFOS limit, on the yearly-average basis EPA uses

systems that have reached the lead action level

systems with a health-based violation since 2016

System population figures are summed from EPA registry records and can overlap where wholesalers and retail systems serve the same people. They are not a Census county-population estimate.

Water systems in this county

All 36 active community systems in the available county records, sorted by record completeness. Scroll the table to explore more systems.

Water system	People served	PFAS survey results	PFAS found	Health-based violations	Lead, 9 in 10 homes at or below
City of Daly City CA4110013	104,901	525	0	0	0 ppbbelow the action level
California Water Service - San Mateo CA4110008	102,348	120	0	0	4.4 ppbbelow the action level
City of Redwood City CA4110022	92,819	95	0	0	0 ppbbelow the action level
California Water Service-S San Francisco CA4110009	64,146	180	0	0	4.1 ppbbelow the action level
California Water Service - Bear Gulch CA4110006	61,431	120	0	0	4 ppbbelow the action level
City of San Bruno CA4110023	42,631	360	0	0	0 ppbbelow the action level
North Coast County Water Dist CA4110025	38,546	120	0	0	0 ppbbelow the action level
Estero Municipal Improvement District CA4110021	36,556	120	0	0	0 ppbbelow the action level
California Water Service - San Carlos CA4110007	35,344	120	0	0	5.8 ppbbelow the action level
City of Burlingame CA4110003	31,451	90	0	0	6.3 ppbbelow the action level
Mid-Peninsula Water District CA4110001	30,609	120	0	0	0 ppbbelow the action level
City of East Palo Alto CA4110024	29,519	90	0	0	0 ppbbelow the action level
City of Millbrae CA4110018	22,795	120	0	0	0 ppbbelow the action level
Menlo Park Municipal Water CA4110017	22,362	120	0	0	3.1 ppbbelow the action level
Coastside County Water District CA4110011	18,940	240	0	0	1.6 ppbbelow the action level
Westborough Water District CA4110027	13,486	120	0	0	0 ppbbelow the action level
Town of Hillsborough CA4110016	11,766	120	0	0	0 ppbbelow the action level
Montara Water and Sanitary District CA4110010	6,078	240	0	0	0 ppbbelow the action level
O'Connor Tract Co-Operative Water Co. CA4110019	2,789	0	0	1	0 ppbbelow the action level
Guadalupe Valley Mid CA4110005	1,472	120	6	0	0 ppbbelow the action level
Cuesta la Honda Guild INC CA4110012	915	0	0	4	0 ppbbelow the action level
County Service Area 11 CA4100582	642	0	0	1	0.6 ppbbelow the action level
County Service Area 7 CA4100509	300	0	0	6	2.1 ppbbelow the action level
Camp Loma Mar CA4100529	208	0	0	1	0 ppbbelow the action level
Redwood Terrace Mutual CA4100510	56	0	0	1	7 ppbbelow the action level
Marchi Central Farm CA4100551	50	0	0	1	0 ppbbelow the action level
Puente Housing Solutions CA4100610	28	0	0	1	0 ppbbelow the action level
City of Brisbane CA4110002	3,402	0	0	0	3 ppbbelow the action level
Palo Alto Park Mutual Water Company CA4110020	2,900	0	0	0	2.7 ppbbelow the action level
Camp Jones Gulch CA4100538	357	0	0	0	5.8 ppbbelow the action level
Butano Canyon Mutual CA4100503	150	0	0	0	2.3 ppbbelow the action level
Redwood Glen Camp & Conference Ctr CA4100522	114	0	0	0	2.8 ppbbelow the action level
Portola Improvement Association Mwc CA4100555	90	0	0	0	0 ppbbelow the action level
Bianchi Flowers INC CA4100583	65	0	0	0	0 ppbbelow the action level
Loma Mar Mutual CA4100512	65	0	0	0	0 ppbbelow the action level
Oku Incorporated CA4100540	35	0	0	0	0 ppbbelow the action level

USGS · Monitoring stations

The water, more recently.

Available station readings in San Mateo County, California. Each measurement keeps its time, unit and original source.

These readings describe water at a monitoring station. They do not test your tap, measure PFAS or lead, or determine whether water is safe to drink or swim in.

Recent observations load when this section comes into view.

How these readings update

We check for updates every 10 minutes while this section is visible and show supported observations from the last 48 hours. The time beside a reading is when USGS measured it; the checked time is when our service retrieved the response. We mark a reading more than 6 hours old as older. Provisional observations can change after USGS review. A missing reading does not mean zero or clean water.

Temperature, pH, dissolved oxygen, turbidity, conductivity, streamflow and water level are shown only where a station reports them. Different measurements have different units and sampling intervals. USGS data and documentation.

Your next step

Water testing, reports & local help.

Use these official directories to find your drinking-water agency, a certified laboratory and public water records. We have not yet added an individually reviewed local resource list for this county.

Official national directories

Water testing

Find your state’s private-well program

EPA’s state directory points well owners to local program information. Services and eligibility vary by state and county.

U.S. Environmental Protection Agency
Source reviewed 2026-09-15 · Source updated 2026-08-05

Water testing

Find a certified drinking-water laboratory

Use EPA’s directory to reach your state’s laboratory certification program. EPA does not provide on-request testing of residential drinking water.

U.S. Environmental Protection Agency
Source reviewed 2026-09-15 · Source updated 2026-08-11

Public records

Find your utility’s Consumer Confidence Report

EPA links to community water-system reports and explains how to read them. Look for your actual supplier rather than assuming every address in a county shares one system.

U.S. Environmental Protection Agency
Source reviewed 2026-09-15 · Source updated 2026-09-09

Public records

Explore USGS water observations

Find current and historical observations from USGS monitoring locations, including available stream, lake, and groundwater data. Measurements vary by station and do not replace a test of your household water.

U.S. Geological Survey
Source reviewed 2026-09-15

A county overview cannot identify every property’s water provider. If you use a public water system, confirm its name on your bill and request its annual Consumer Confidence Report. Private wells need their own testing; public-system records do not describe a private well.

Understand water testing and laboratory reports

Resource descriptions are compiled by Tap Water Lookup. Review dates describe our source check, not a new water sample. How we review sources · Suggest a correction

Explore your area

Local coverage in San Mateo County

30ZIP areas in this overview

Explore the water-system records, recent station readings and testing resources on this county page. They describe the systems and stations identified in each section; they are not a separate water test for every community.

Towns and communities

Atherton
Belmont
Brisbane
Daly City
El Granada
Foster City
Half Moon Bay
Hillsborough
La Honda
Loma Mar
Menlo Park
Millbrae
Montara
Moss Beach
Pacifica
Pescadero
Portola Valley
Redwood City
San Bruno
San Carlos
San Mateo
South San Francisco
Woodside

Explore water-system records Find water-testing resources

View ZIP areas and understand coverage

94002Belmont
94005Brisbane
94010Hillsborough
94014Daly City
94015Daly City
94018El Granada
94019Half Moon Bay
94020La Honda
94021Loma Mar
94025Menlo Park
94027Atherton
94028Portola Valley
94030Millbrae
94037Montara
94038Moss Beach
94044Pacifica
94060Pescadero
94061Redwood City
94062Woodside
94063Redwood City
94065Redwood City
94066San Bruno
94070San Carlos
94074
94080South San Francisco
94128South San Francisco
94401San Mateo
94402San Mateo
94403San Mateo
94404Foster City

These Census ZIP Code Tabulation Areas are grouped here by their largest county overlap. A ZIP area can cross county lines and contain several water suppliers or private wells. Place labels reflect Census geography, not verified postal city names or utility service boundaries.

Records for these areas are currently presented in this county overview rather than individual ZIP reports. An unpublished report does not mean there are no water records. Confirm your supplier on your water bill; if you use a private well, testing your own well is the relevant next step.

Beyond this county page

Keep reading. Compare nearby.

PFASChoosing a PFAS filterPFAS was found in 1 of the 19 systems EPA surveyed here. See how to check a filter’s certified PFAS reduction.LeadChoosing a lead filter16 systems here have reached the lead action level. See how to check a filter’s lead-reduction certification.Your utilityFind your annual water reportConfirm the supplier on your bill, then read its Consumer Confidence Report for local results.

Counties near San Mateo County

All California counties

Sources and scope

EPA UCMR 5 occurrence data, samples collected 2023-01-03 – 2026-06-17, final release, August 2026 (file dated Aug 28, 2026); EPA SDWIS via ECHO, 2026Q2 extract (file dated Jul 9, 2026); EPA service-area boundaries v3.0; Census 2020 ZCTAs. Database prepared 2026-09-03.

Counts cover the systems that report this county to EPA. A water system may cross county lines. "Found" means at least one result at or above the laboratory reporting level; it is not a compliance finding.

Compiled by Tap Water Lookup from the sources identified on this page. Read the methodology and review process.