Public water system · CA5000164
ActiveModesto Reservoir
At a glance
Modesto Reservoir (PWSID CA5000164) is an active transient non-community water system in Stanislaus County, California. It reports serving 25 people through 4 service connections. Its primary water source is groundwater, and EPA lists it as owned by a local government. EPA's records list 8 violations for this system; 4 are health-based, and the most recent began in August 2007.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
25
Service connections
4
Primary source
GW
Groundwater
System type
TNCWS
Transient non-community water system
System record
How does Modesto Reservoir compare with other water systems in Stanislaus County?
By EPA's size categories, Modesto Reservoir is a very small system (500 people or fewer). Stanislaus County has 191 active public water systems. Its population served is well below the county average of 2,684 people per system, and accounts for less than 0.1% of the 512,656 people reported by systems filed under the county. Across California, the 7,479 active systems average 5,706 people each. Nationally, the average active transient non-community water system reports serving 144 people, so Modesto Reservoir is well below that figure.
What does “transient non-community water system” mean?
A transient non-community water system serves places where people do not stay long, such as gas stations and campgrounds, and regularly serves at least 25 people a day for at least 60 days a year. California has 3,016 active transient non-community water systems, 40% of the state's 7,479 active systems. Groundwater means the system draws its water from wells or springs fed by underground aquifers. 6,179 California systems (83%) list groundwater as their primary source.
Who owns and regulates Modesto Reservoir?
EPA lists Modesto Reservoir as owned by a local government. 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. 57 of the 191 active systems in Stanislaus County (30%) are also owned by a local government.
Does Modesto Reservoir have drinking water violations?
EPA's records list 8 violations for this system; 4 are health-based, and the most recent began in August 2007. The violations listed here began between October 1982 and August 2007. By type: 4 contaminant level above the legal limit and 4 public notice, recordkeeping or other. The contaminant or rule involved most often is Total coliform bacteria (TCR) (4 of them). EPA lists 4 as resolved and 4 as archived. 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. Archived means the violation was not marked resolved but is more than five years past the end of the noncompliance period, so it no longer counts toward current compliance status.
| Began | Violation | Contaminant or rule | Health-based | Status |
|---|---|---|---|---|
| 2007-08-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 2004-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 2003-08-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 2002-05-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1983-07-01 | Public notice, recordkeeping or otherNotification, Public · code 06 | Not reported | No | Archived |
| 1983-04-01 | Public notice, recordkeeping or otherNotification, Public · code 06 | Not reported | No | Archived |
| 1983-01-01 | Public notice, recordkeeping or otherNotification, Public · code 06 | Not reported | No | Archived |
| 1982-10-01 | Public notice, recordkeeping or otherNotification, Public · code 06 | Not reported | No | Archived |
All 8 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.
Modesto Reservoir: frequently asked questions
Who runs Modesto Reservoir?
Modesto Reservoir (PWSID CA5000164) is a transient non-community water system owned by a local government. It is regulated by the CA state drinking water program.
How many people does Modesto Reservoir serve?
Modesto Reservoir reports serving 25 people through 4 service connections in Stanislaus County, California.
Where does Modesto Reservoir get its water?
EPA SDWIS lists this system's primary water source as groundwater. Groundwater means the system draws its water from wells or springs fed by underground aquifers.
Does Modesto Reservoir have any drinking water violations?
EPA's records list 8 violations for this system; 4 are health-based, and the most recent began in August 2007. 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 Modesto Reservoir'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. EPA's records list 8 violations for this system; 4 are health-based, and the most recent began in August 2007. For current results, consult EPA ECHO, or the CA state drinking water program.
Where can I find Modesto Reservoir's water quality report?
The annual Consumer Confidence Report requirement applies to community water systems. Modesto Reservoir is a transient non-community water system, so it is not required to publish one; like every public water system, it must notify the people it serves about violations under EPA's public notification rules.
Other water systems in Stanislaus County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Modesto, City of | Stanislaus | 218,771 | Community | Purchased surface water |
| Turlock, City of | Stanislaus | 72,682 | Community | Purchased surface water |
| Ceres, City of | Stanislaus | 54,513 | Community | Purchased surface water |
| Patterson, City of | Stanislaus | 24,977 | Community | Groundwater |
| Riverbank, City of | Stanislaus | 24,834 | Community | Groundwater |
| Oakdale, City of | Stanislaus | 23,235 | Community | Groundwater |
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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, “Modesto Reservoir, PWSID CA5000164, California”, https://aquacensus.com/water-systems/california/modesto-reservoir-ca5000164 (data as of October 1, 2026).