WY / Yellowstone National Park
WY · Tap water records
Yellowstone National Park tap water, in plain English
Here is what the EPA's own data shows about tap water in Yellowstone National Park. According to EPA SDWIS data retrieved June 2026, Yellowstone National Park is served by 1 active community water system, together reported to serve about 2,600 people.
As of June 2026, EPA records show 5 violations across the community water system(s) serving Yellowstone National Park, going back to the earliest EPA record. None were health-based; the records are monitoring or reporting violations (a required test or report was late or missed). Each is listed by system below, with its status.
What the EPA has on record, by system
Ynp-Mammoth Hot Springs
2,600 served · surface water · PWSID WY5680092 - Monitoring Surface Water Treatment Rule: a monitoring or reporting violation (a required test or report was late or missed — not a measured exceedance), recorded 3 times in August 2023. EPA records do not show all of these as returned to compliance.
- Monitoring TTHM: a monitoring or reporting violation (a required test or report was late or missed — not a measured exceedance), recorded once in June 2017. All have since returned to compliance, per EPA records.
- Monitoring Total Haloacetic Acids (HAA5): a monitoring or reporting violation (a required test or report was late or missed — not a measured exceedance), recorded once in June 2017. All have since returned to compliance, per EPA records.
What this means
A health-based violation means a contaminant was recorded above the limit the EPA tracks for it. A monitoring or reporting violation means a required test or report was late or missed — not that a contaminant was measured above a limit. “Returned to compliance” means the EPA recorded the issue as resolved.
This page summarizes the EPA's own records and does not assess whether your water is safe to drink. For the most current details, you can verify every record directly with the EPA, and contact your water system with questions.
Source: U.S. EPA Envirofacts SDWIS, retrieved June 2026. Records cover the EPA's full reporting history for these systems. Verify at EPA ECHO.