PlainWater
States → California

Community Water System · PWS CA4010002

Atascadero Mutual Water Co

Atascadero, California 93422 - drinking water served from groundwater sources to 30,618 people, tracked in EPA SDWIS and UCMR5.

30,618
People served
3
EPA violations
2
Health-based
5 PFAS
UCMR5 result

The verdict

EPA records 3 drinking-water violations at Atascadero Mutual Water Co, 67% of them health-based - below the California per-system average, and UCMR5 testing detected 5 PFAS compounds.

3
Total EPA violations on record
67%
Health-based (MCL / treatment failure)
30,618
People served by this system
5
PFAS compounds detected (UCMR5)

Water Quality Snapshot: Atascadero Mutual Water Co

Atascadero Mutual Water Co is a private-owned community water system that delivers drinking water to 30,618 residents in Atascadero, California (San Luis Obispo County) through 10,961 service connections. Its water is drawn from groundwater sources. EPA's Safe Drinking Water Information System records 3 total violations for this system , of which 2 (67%) are health-based, meaning a contaminant exceeded an EPA Maximum Contaminant Level or a required treatment technique failed. The most recent violation on record dates to 1993.

The most frequently cited contaminant at this system is Surface Water Treatment Rule, recorded in 2 violations (TT, health-based). Under EPA's UCMR5 PFAS monitoring program, 5 PFAS compounds were detected in samples collected from this system, with a maximum reported concentration of 22.3 ppt (parts per trillion). PFAS are persistent synthetic chemicals linked to health effects at very low exposure levels.

Across California, EPA tracks 7,249 public water systems serving 42,404,883 people, with 153,308 cumulative violations and 63,983 health-based violations on record. About 89% of systems in the state carry at least one violation, and state-wide the average per system is 21.1 violations. Statewide, 447 of 694 UCMR5-tested systems have reported PFAS detections (64.4%).

Atascadero Mutual Water Co's 3 violations sit below the California average.

All figures above are sourced directly from EPA SDWIS and UCMR5 public data releases and are updated as EPA publishes new reporting cycles.

PFAS Detected

5 PFAS "forever chemicals" detected in testing under EPA's UCMR5 monitoring program.

Population Served
30,618
Total Violations
3
Health-Based Violations
2
Water Source
Groundwater

System Details

System Type
Community
Owner Type
Private
Connections
10,961
County
San Luis Obispo
School/Daycare
No
MCL Violations
0
Monitoring Violations
0
Treatment Tech Violations
2

Violation History

Contaminant violations recorded by EPA.

Contaminant Category Count Latest
Surface Water Treatment Rule TT 2 1993

PFAS Testing Results (UCMR5)

Results from EPA's Fifth Unregulated Contaminant Monitoring Rule. 18 of 232 samples detected PFAS.

Contaminant Date Result MRL Status
PFNA 5/30/2023 <4.00 ppt 4.00 ppt Not Detected
6:2 FTS 5/30/2023 <5.00 ppt 5.00 ppt Not Detected
PFBS 5/30/2023 3.90 ppt 3.00 ppt Detected
PFHpA 5/30/2023 <3.00 ppt 3.00 ppt Not Detected
PFHxS 5/30/2023 4.30 ppt 3.00 ppt Detected
PFOS 5/30/2023 21.00 ppt 4.00 ppt Detected
PFDA 5/30/2023 <3.00 ppt 3.00 ppt Not Detected
PFDoA 5/30/2023 <3.00 ppt 3.00 ppt Not Detected
PFHxA 5/30/2023 <3.00 ppt 3.00 ppt Not Detected
PFUnA 5/30/2023 <2.00 ppt 2.00 ppt Not Detected
11Cl-PF3OUdS 5/30/2023 <5.00 ppt 5.00 ppt Not Detected
9Cl-PF3ONS 5/30/2023 <2.00 ppt 2.00 ppt Not Detected
ADONA 5/30/2023 <3.00 ppt 3.00 ppt Not Detected
PFOA 5/30/2023 8.40 ppt 4.00 ppt Detected
PFBA 5/30/2023 7.40 ppt 5.00 ppt Detected
NFDHA 5/30/2023 <20.00 ppt 20.00 ppt Not Detected
HFPO-DA 5/30/2023 <5.00 ppt 5.00 ppt Not Detected
PFPeS 5/30/2023 <4.00 ppt 4.00 ppt Not Detected
PFEESA 5/30/2023 <3.00 ppt 3.00 ppt Not Detected
PFMBA 5/30/2023 <3.00 ppt 3.00 ppt Not Detected
PFPeA 5/30/2023 <3.00 ppt 3.00 ppt Not Detected
PFMPA 5/30/2023 <4.00 ppt 4.00 ppt Not Detected
8:2 FTS 5/30/2023 <5.00 ppt 5.00 ppt Not Detected
4:2 FTS 5/30/2023 <3.00 ppt 3.00 ppt Not Detected
PFHpS 5/30/2023 <3.00 ppt 3.00 ppt Not Detected
8:2 FTS 4/19/2023 <5.00 ppt 5.00 ppt Not Detected
4:2 FTS 4/19/2023 <3.00 ppt 3.00 ppt Not Detected
PFPeS 4/19/2023 <4.00 ppt 4.00 ppt Not Detected
PFMBA 4/19/2023 <3.00 ppt 3.00 ppt Not Detected
PFEESA 4/19/2023 <3.00 ppt 3.00 ppt Not Detected
NFDHA 4/19/2023 <20.00 ppt 20.00 ppt Not Detected
PFMPA 4/19/2023 <4.00 ppt 4.00 ppt Not Detected
PFHpS 4/19/2023 <3.00 ppt 3.00 ppt Not Detected
PFPeA 4/19/2023 <3.00 ppt 3.00 ppt Not Detected
NMeFOSAA 4/19/2023 <6.00 ppt 6.00 ppt Not Detected
PFTrDA 4/19/2023 <7.00 ppt 7.00 ppt Not Detected
PFTA 4/19/2023 <8.00 ppt 8.00 ppt Not Detected
6:2 FTS 4/19/2023 <5.00 ppt 5.00 ppt Not Detected
PFOS 4/19/2023 <4.00 ppt 4.00 ppt Not Detected
NEtFOSAA 4/19/2023 <5.00 ppt 5.00 ppt Not Detected
PFDoA 4/19/2023 <3.00 ppt 3.00 ppt Not Detected
PFDA 4/19/2023 <3.00 ppt 3.00 ppt Not Detected
PFHpA 4/19/2023 <3.00 ppt 3.00 ppt Not Detected
PFBA 4/19/2023 <5.00 ppt 5.00 ppt Not Detected
PFBS 4/19/2023 <3.00 ppt 3.00 ppt Not Detected
PFHxS 4/19/2023 3.20 ppt 3.00 ppt Detected
PFNA 4/19/2023 <4.00 ppt 4.00 ppt Not Detected
PFOA 4/19/2023 <4.00 ppt 4.00 ppt Not Detected
PFHxA 4/19/2023 <3.00 ppt 3.00 ppt Not Detected
PFUnA 4/19/2023 <2.00 ppt 2.00 ppt Not Detected

Verify This Water System

The figures above are aggregated from EPA's public databases. To verify the underlying records, or to file a complaint, request a Consumer Confidence Report, or check current monitoring status, go directly to the federal and state regulators that enforce the Safe Drinking Water Act for Atascadero Mutual Water Co.

Federal Source of Truth

EPA SDWIS, Federal Reports

EPA's Safe Drinking Water Information System (SDWIS) holds the federal compliance record for every regulated public water system. Open the system-level report by PWS ID:

View PWS ID CA4010002 on SDWIS

Source: EPA SDWIS Federal Reports Search

State Regulator

California Drinking Water Authority

California State Water Resources Control Board, Division of Drinking Water is the primacy agency that licenses and inspects Atascadero Mutual Water Co under EPA-delegated authority.

Open CA regulator portal

Source: California State Water Resources Control Board, Division of Drinking Water

Violation Timeline

Each row links to the EPA SDWIS public record for verification. Cross-reference the contaminant code on EPA's federal report to see violation dates, return-to-compliance status, and enforcement actions.

Year (latest) Contaminant Category Count EPA Record
1993 Surface Water Treatment Rule TT 2 SDWIS / CA4010002 / 0200

How Atascadero Mutual Water Co Compares

Cross-reference this system's record against state averages and the federal MCL framework for context.

Metric Atascadero Mutual Water Co California avg Federal benchmark
Total violations 3 21.1 SDWA compliance, any non-zero count is a recorded breach
Health-based violations 2 8.8 Indicates a contaminant exceeded a federal MCL
PFAS detection 5 compounds 64.4% EPA final rule (2024): PFOA/PFOS MCL = 4.0 ppt
Population served 30,618 5,850 Sizing context for compliance burden

Sources: EPA SDWIS and EPA National Primary Drinking Water Regulations (40 CFR Part 141). State averages computed across 7,249 regulated public water systems in California.

Federal MCL reference, Safe Drinking Water Act thresholds ▼
Contaminant Federal MCL / Action Level Note
Lead 0 mg/L (Action Level: 0.015 mg/L) Lead and Copper Rule treatment technique
Arsenic 0.010 mg/L (10 ppb) Health-based MCL since 2006
Total Coliform Treatment technique (RTCR) Indicator organism, monitoring trigger
PFOA / PFOS (PFAS) 4.0 ppt each (final 2024 rule) Compliance deadline 2029 (EPA proposed extending to 2031, not yet final as of May 2026)
Nitrate (as N) 10 mg/L Acute health risk for infants

Frequently Asked Questions

Is Atascadero Mutual Water Co water safe to drink? ▼
Atascadero Mutual Water Co (PWS ID: CA4010002) has 3 recorded violations in the EPA SDWIS database. PFAS contamination has been detected in UCMR5 testing, with 5 PFAS compounds found. This system serves 30,618 people using Groundwater sources.
How many people does Atascadero Mutual Water Co serve? ▼
Atascadero Mutual Water Co serves 30,618 people in Atascadero, California. It is a Private-owned system using Groundwater water sources with 10,961 service connections.
What type of violations does Atascadero Mutual Water Co have? ▼
Atascadero Mutual Water Co has 3 total violations: 2 health-based violations (MCL exceedances or treatment failures), 0 monitoring/reporting violations, and 2 treatment technique violations. Health-based violations indicate contaminant levels exceeded EPA safe limits.
Has PFAS been detected in Atascadero Mutual Water Co water? ▼
Yes. UCMR5 testing detected 5 PFAS compounds in Atascadero Mutual Water Co's water supply: PFBS, PFHxS, PFOS, PFOA, PFBA. PFAS are persistent "forever chemicals" that do not break down in the environment.
What water source does Atascadero Mutual Water Co use? ▼
Atascadero Mutual Water Co uses Groundwater as its primary water source. It is classified as a Community Water System (CWS), serving residential populations year-round.
Where does this data come from? ▼
All data comes from the EPA Safe Drinking Water Information System (SDWIS) and the UCMR5 PFAS monitoring program. SDWIS tracks compliance for all public water systems regulated under the Safe Drinking Water Act.
Data Sources: EPA Safe Drinking Water Information System (SDWIS), Q4 2025. PFAS data from EPA UCMR5 monitoring program (2023-2025). This data is provided for informational purposes only.

Read our methodology - how this data is sourced, computed, and verified.

Data sourced from EPA SDWIS and UCMR5 PFAS monitoring data. See our methodology for details. Retrieved and formatted by PlainWater Editorial

Every figure on PlainWater is rendered directly from EPA SDWIS drinking-water data, no number is typed in by an editor. This system's figures are rendered directly from EPA SDWIS data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.