MAMMOTH LAKES, CA · Mono County
MAMMOTH CWD Water System
Consumer Confidence Report status
MAMMOTH CWD must publish a Consumer Confidence Report — the annual drinking water quality report covering calendar year 2026 — by July 1, 2027.
As of August 1, 2026, EPA's federal records show no open violations for MAMMOTH CWD.
Data sourced from the EPA ECHO database (SDWA bulk download), last refreshed August 1, 2026. This is a record-keeping and public-information tool — it does not replace California’s official records. Always confirm current status with California before making decisions based on this information.
System facts
- System ID (PWSID)
- CA2610001
- System type
- Community Water System
- Population served
- 8,234
- Service connections
- 3,818
- Ownership
- local government
- Water source
- surface water (rivers, lakes, or reservoirs)
MAMMOTH CWD is one of 278 community water systems in California in the 3,301 to 10,000 people size category, serving 8,234 people from surface water.
As of August 1, 2026, its federal record holds 4 entries between 1991 and 2023, all of which EPA lists as closed. Nothing has been added since 2023.
Of the 4, 2 are monitoring and reporting requirements — the category that accounts for about four in five of all violations in EPA's national dataset — rather than findings about the water itself. The record involves the Stage 2 Disinfectants and Disinfection Byproducts Rule, the Total Coliform Rules, and the Surface Water Treatment Rules.
Violation history
Monitoring and Reporting (DBP)
—Total Haloacetic Acids (HAA5)
January 1, 2023 – December 31, 2023
ResolvedMonitoring and Reporting (DBP)
—TTHM
January 1, 2023 – December 31, 2023
ResolvedMaximum Contaminant Level Violation, Monthly (TCR)
Health-basedColiform (TCR)
September 1, 1992 – September 30, 1992
ResolvedTreatment Technique (SWTR and GWR)
Health-basedSurface Water Treatment Rule
June 1, 1991 – June 30, 1991
Resolved
Resolved addressed and confirmed by the state
| Period | Violation | Contaminant / rule | Health-based | Status |
|---|---|---|---|---|
| January 1, 2023 – December 31, 2023 | Monitoring and Reporting (DBP) | Total Haloacetic Acids (HAA5) | — | Resolved |
| January 1, 2023 – December 31, 2023 | Monitoring and Reporting (DBP) | TTHM | — | Resolved |
| September 1, 1992 – September 30, 1992 | Maximum Contaminant Level Violation, Monthly (TCR) | Coliform (TCR) | Health-based | Resolved |
| June 1, 1991 – June 30, 1991 | Treatment Technique (SWTR and GWR) | Surface Water Treatment Rule | Health-based | Resolved |
Resolved addressed and confirmed by the state
Enforcement actions
- July 10, 2024State Compliance achieved9 linked violations
- November 8, 1993State Administrative/Compliance Order without penalty issued1 linked violation
Common questions
Is MAMMOTH CWD required to publish a Consumer Confidence Report?
- Yes. MAMMOTH CWD is a community water system, and federal rules (40 CFR 141 Subpart O) require every community water system to publish a Consumer Confidence Report each year.
When is MAMMOTH CWD’s next Consumer Confidence Report due?
- MAMMOTH CWD’s next Consumer Confidence Report is due by July 1, 2027. The report covers calendar year 2026.
Does MAMMOTH CWD have any open drinking water violations on record?
- As of August 1, 2026, EPA's federal records show no open violations for MAMMOTH CWD.
What is a Consumer Confidence Report?
- A Consumer Confidence Report (CCR) is the annual drinking water quality report that community water systems must provide to the people they serve. It lists the contaminants detected in the system’s water during the year, where the water comes from, and how the results compare with federal limits. EPA’s revised CCR rule takes effect January 1, 2027, and the first reports in the new format are due July 1, 2027.
Contact
BUSBY, MARK
760-934-2596
MAMMOTH LAKES, CA 93546