Public water system · CA2600729
ActiveMammoth Lakes Basin
At a glance
Mammoth Lakes Basin (PWSID CA2600729) is an active transient non-community water system in Mono County, California. It reports serving 1,000 people through 56 service connections. Its primary water source is groundwater, and EPA lists it as owned by the federal government. EPA's records list one violation for this system; it is health-based, and the most recent began in August 2005.
Dataset updated . Source: EPA SDWIS/ECHO public records.
Population served
1,000
Service connections
56
Primary source
GW
Groundwater
System type
TNCWS
Transient non-community water system
System record
How does Mammoth Lakes Basin compare with other water systems in Mono County?
By EPA's size categories, Mammoth Lakes Basin is a small system (501 to 3,300 people). Mono County has 84 active public water systems, and Mammoth Lakes Basin is the 6th-largest of them by population served. Its population served is about 136% above the county average of 424 people per system, and accounts for 2.8% of the 35,602 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 Mammoth Lakes Basin is about 6.9 times 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 Mammoth Lakes Basin?
EPA lists Mammoth Lakes Basin as owned by the federal 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. 16 of the 84 active systems in Mono County (19%) are also owned by the federal government.
Does Mammoth Lakes Basin have drinking water violations?
EPA's records list one violation for this system; it is health-based, and the most recent began in August 2005. By type: 1 contaminant level above the legal limit. The contaminant or rule involved is Total coliform bacteria (TCR). EPA lists 1 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 |
|---|---|---|---|---|
| 2005-08-01 | Contaminant level above the legal limitMaximum Contaminant Level Violation, Monthly (TCR) · code 22 | Total coliform bacteria (TCR)code 3100 | Yes | Resolved |
The one violation in EPA's records.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.
Mammoth Lakes Basin: frequently asked questions
Who runs Mammoth Lakes Basin?
Mammoth Lakes Basin (PWSID CA2600729) is a transient non-community water system owned by the federal government. It is regulated by the CA state drinking water program.
How many people does Mammoth Lakes Basin serve?
Mammoth Lakes Basin reports serving 1,000 people through 56 service connections in Mono County, California.
Where does Mammoth Lakes Basin 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 Mammoth Lakes Basin have any drinking water violations?
EPA's records list one violation for this system; it is health-based, and the most recent began in August 2005. 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 Mammoth Lakes Basin'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 one violation for this system; it is health-based, and the most recent began in August 2005. For current results, consult EPA ECHO, or the CA state drinking water program.
Where can I find Mammoth Lakes Basin's water quality report?
The annual Consumer Confidence Report requirement applies to community water systems. Mammoth Lakes Basin 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 Mono County
| Water system | County | Population served | Type | Source |
|---|---|---|---|---|
| Mammoth Cwd | Mono | 8,234 | Community | Surface water |
| Mammoth Mountain Ski Area - Outpost 14 | Mono | 7,736 | Non-transient non-community | Groundwater |
| June Lake PUD - Down Canyon | Mono | 2,810 | Community | Surface water |
| June Lake PUD Village | Mono | 2,763 | Community | Surface water |
| Usmc/Mtn Warfare Trng Ctr - Bridgeport | Mono | 1,200 | Community | Groundwater |
| East Fork Campground | Mono | 750 | Transient non-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, “Mammoth Lakes Basin, PWSID CA2600729, California”, https://aquacensus.com/water-systems/california/mammoth-lakes-basin-ca2600729 (data as of October 1, 2026).