Public water system · CA5010010
ActiveModesto, City of
At a glance
City of Modesto (PWSID CA5010010) is an active community water system in Stanislaus County, California. It reports serving 218,771 people through 70,793 service connections. Its primary water source is purchased surface water, and EPA lists it as owned by a local government. Of the 12 most recent violations in EPA's records, 10 are health-based, and the most recent began in August 2013.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
218,771
Service connections
70,793
Primary source
SWP
Purchased surface water
System type
CWS
Community water system
System record
How does City of Modesto compare with other water systems in Stanislaus County?
By EPA's size categories, City of Modesto is a very large system (more than 100,000 people). Stanislaus County has 191 active public water systems, and City of Modesto is the largest of them by population served. Its population served is about 82 times the county average of 2,684 people per system, and accounts for 43% 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 community water system reports serving 6,703 people, so City of Modesto is about 33 times 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. Purchased surface water means the system buys surface water from another public water system rather than drawing its own. 506 California systems (6.8%) list purchased surface water as their primary source.
Who owns and regulates City of Modesto?
EPA lists City of Modesto 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 City of Modesto have drinking water violations?
Of the 12 most recent violations in EPA's records, 10 are health-based, and the most recent began in August 2013. The violations listed here began between July 1993 and August 2013. By type: 10 contaminant level above the legal limit and 2 monitoring and reporting. The contaminant or rule involved most often is Total coliform bacteria (TCR) (9 of them). 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 |
|---|---|---|---|---|
| 2013-08-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Single Sample · code 01 | Nitratecode 1040 | Yes | Resolved |
| 2007-03-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Nitratecode 1040 | Yes | Resolved |
| 2001-01-01 | Monitoring and reportingMonitoring, Repeat Minor (TCR) · code 26 | Total coliform bacteria (TCR)code 3100 | No | Resolved |
| 1996-02-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1995-09-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1995-05-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1994-10-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1994-08-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1994-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
| 1993-11-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Average · code 02 | Combined Uraniumcode 4006 | Yes | Resolved |
| 1993-11-01 | Monitoring and reportingMonitoring, Repeat Minor (TCR) · code 26 | Total coliform bacteria (TCR)code 3100 | No | Resolved |
| 1993-07-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | 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.
City of Modesto: frequently asked questions
Who runs City of Modesto?
City of Modesto (PWSID CA5010010) is a community water system owned by a local government. It is regulated by the CA state drinking water program.
How many people does City of Modesto serve?
City of Modesto reports serving 218,771 people through 70,793 service connections in Stanislaus County, California.
Where does City of Modesto get its water?
EPA SDWIS lists this system's primary water source as purchased surface water. Purchased surface water means the system buys surface water from another public water system rather than drawing its own.
Does City of Modesto have any drinking water violations?
Of the 12 most recent violations in EPA's records, 10 are health-based, and the most recent began in August 2013. 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 City of Modesto'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, 10 are health-based, and the most recent began in August 2013. For current results, consult the system's annual water quality report, EPA ECHO, or the CA state drinking water program.
Where can I find City of Modesto's water quality report?
As a community water system, City of Modesto 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 Stanislaus County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| 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 |
| City of Modesto - Salida | Stanislaus | 14,537 | 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, “Modesto, City of, PWSID CA5010010, California”, https://aquacensus.com/water-systems/california/modesto-city-of-ca5010010 (data as of October 1, 2026).