Public water system · CA4100510
ActiveRedwood Terrace Mutual
At a glance
Redwood Terrace Mutual (PWSID CA4100510) is an active community water system in San Mateo County, California. It reports serving 56 people through 18 service connections. Its primary water source is groundwater under influence of surface water, and EPA lists it as privately owned. Of the 12 most recent violations in EPA's records, one is health-based, and the most recent began in July 2024.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
56
Service connections
18
Primary source
GU
Groundwater under influence of surface water
System type
CWS
Community water system
System record
How does Redwood Terrace Mutual compare with other water systems in San Mateo County?
By EPA's size categories, Redwood Terrace Mutual is a very small system (500 people or fewer). San Mateo County has 51 active public water systems. Its population served is well below the county average of 15,363 people per system, and accounts for less than 0.1% of the 783,522 people reported by systems filed under the county. Across California, the 7,479 active systems average 5,706 people each. Nationally, the average active community water system reports serving 6,703 people, so Redwood Terrace Mutual is well below that figure.
What does “community water system” mean?
A community water system serves at least 15 connections used by year-round residents, or regularly serves at least 25 year-round residents. Homes, apartments and mobile-home parks are served by these. California has 2,997 active community water systems, 40% of the state's 7,479 active systems. Groundwater under the influence of surface water is well or spring water that the regulator has found to be affected by nearby surface water, so it is regulated under the surface-water treatment rules. 105 California systems (1.4%) list groundwater under influence of surface water as their primary source.
Who owns and regulates Redwood Terrace Mutual?
EPA lists Redwood Terrace Mutual as privately owned. The CA state drinking water program is its primacy agency, the regulator with primary enforcement responsibility for the system under the Safe Drinking Water Act. 27 of the 51 active systems in San Mateo County (53%) are also privately owned.
Does Redwood Terrace Mutual have drinking water violations?
Of the 12 most recent violations in EPA's records, one is health-based, and the most recent began in July 2024. The violations listed here began between January 2009 and July 2024. By type: 11 monitoring and reporting and 1 required treatment not met. The contaminants or rules involved are Lead and Copper Rule, Revised Total Coliform Rule, Nitrate-Nitrite and Total coliform bacteria (TCR). EPA lists 12 as resolved. Resolved means at least one resolving action is on record: the system returned to compliance, the rule no longer applies, or no further action was needed.
| Began | Violation | Contaminant or rule | Health-based | Status |
|---|---|---|---|---|
| 2024-07-01 | Monitoring and reportingFollow-up Or Routine LCR Tap M/R · code 52 | Lead and Copper Rulecode 5000 | No | Resolved |
| 2019-06-01 | Required treatment not metTreatment Technique, Level 1 Assessment (RTCR) · code 2A | Revised Total Coliform Rulecode 8000 | Yes | Resolved |
| 2019-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Nitrate-Nitritecode 1038 | No | Resolved |
| 2010-06-01 | Monitoring and reportingMonitoring, Routine Major (TCR) · code 23 | Total coliform bacteria (TCR)code 3100 | No | Resolved |
| 2009-04-01 | Monitoring and reportingMonitoring, Regular · code 03 | Radium-228code 4030 | No | Resolved |
| 2009-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Benzenecode 2990 | No | Resolved |
| 2009-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Picloramcode 2040 | No | Resolved |
| 2009-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Ethylbenzenecode 2992 | No | Resolved |
| 2009-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Dinosebcode 2041 | No | Resolved |
| 2009-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Toxaphenecode 2020 | No | Resolved |
| 2009-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Oxamylcode 2036 | No | Resolved |
| 2009-01-01 | Monitoring and reportingMonitoring, Regular · code 03 | Heptachlorcode 2065 | No | Resolved |
The 12 most recent violations in EPA's records, newest first.Labels and codes come from EPA's SDWIS reference tables. A monitoring or reporting violation means a required test or report was missed or late; it does not by itself mean a contaminant was found. "Health-based" marks violations of a legal limit or required treatment.
Redwood Terrace Mutual: frequently asked questions
Who runs Redwood Terrace Mutual?
Redwood Terrace Mutual (PWSID CA4100510) is a community water system privately owned. It is regulated by the CA state drinking water program.
How many people does Redwood Terrace Mutual serve?
Redwood Terrace Mutual reports serving 56 people through 18 service connections in San Mateo County, California.
Where does Redwood Terrace Mutual get its water?
EPA SDWIS lists this system's primary water source as groundwater under influence of surface water. Groundwater under the influence of surface water is well or spring water that the regulator has found to be affected by nearby surface water, so it is regulated under the surface-water treatment rules.
Does Redwood Terrace Mutual have any drinking water violations?
Of the 12 most recent violations in EPA's records, one is health-based, and the most recent began in July 2024. A monitoring or reporting violation means a required test or report was missed or late; it does not by itself mean a contaminant was found.
Is Redwood Terrace Mutual's water safe to drink?
AquaCensus shows EPA compliance records, not current water test results, so it cannot say whether the water is safe at a given moment. Of the 12 most recent violations in EPA's records, one is health-based, and the most recent began in July 2024. For current results, consult the system's annual water quality report, EPA ECHO, or the CA state drinking water program.
Where can I find Redwood Terrace Mutual's water quality report?
As a community water system, Redwood Terrace Mutual must deliver an annual water quality report, called a Consumer Confidence Report, to its customers by July 1 each year, covering the previous calendar year. The system can provide a copy on request.
Other water systems in San Mateo County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| City of Daly City | San Mateo | 104,901 | Community | Purchased surface water |
| California Water Service - San Mateo | San Mateo | 102,348 | Community | Purchased surface water |
| City of Redwood City | San Mateo | 92,819 | Community | Purchased surface water |
| California Water Service-S San Francisco | San Mateo | 64,146 | Community | Purchased surface water |
| California Water Service - Bear Gulch | San Mateo | 61,431 | Community | Surface water |
| City of San Bruno | San Mateo | 42,631 | Community | Purchased surface water |
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About this data
Source: U.S. EPA Safe Drinking Water Information System (SDWIS) and SDWA violation records, via EPA ECHO, as published October 1, 2026 — AquaCensus refreshes it quarterly. See the methodology for how records are matched, cleaned and scored.
Cite as: AquaCensus, “Redwood Terrace Mutual, PWSID CA4100510, California”, https://aquacensus.com/water-systems/california/redwood-terrace-mutual-ca4100510 (data as of October 1, 2026).