Diablo Water District
As of June 2026, EPA records show no reported violations for this system in the period covered. This is not a guarantee about every substance, or about the water inside your home's plumbing.
CA / Oakley
CA · Tap water records
Oakley tap water, in plain English
Here is what the EPA's own data shows about tap water in Oakley. According to EPA SDWIS data retrieved June 2026, Oakley is served by 8 active community water systems, together reported to serve about 44,728 people.
As of June 2026, EPA records show 107 violations across the community water system(s) serving Oakley, going back to the earliest EPA record. 100 of these are classified by the EPA as health-based (a contaminant recorded above the limit the EPA tracks); the rest are monitoring or reporting violations. Each is listed by system below, with its status.
- 8Community water systems
- ~44,728People served (EPA-reported)
- June 2026EPA records reviewed through
What the EPA has on record, by system
Willow Park Marina
- Health-based Arsenic: a health-based violation (a contaminant recorded above the limit the EPA tracks), recorded 31 times between January 2021 and October 2025. The EPA record lists a level of 0.011 MG/L; the limit (MCL) is 0.01 MG/L. EPA records do not show all of these as returned to compliance.
Delta Mutual Water Company
- Health-based Arsenic: a health-based violation (a contaminant recorded above the limit the EPA tracks), recorded 40 times between January 2020 and July 2025. The EPA record lists a level of 0.012 MG/L; the limit (MCL) is 0.01 MG/L. EPA records do not show all of these as returned to compliance.
- Monitoring Nitrate: a monitoring or reporting violation (a required test or report was late or missed — not a measured exceedance), recorded 2 times in January 2017. All have since returned to compliance, per EPA records.
Camino Mobilehome
- Monitoring Nitrate: a monitoring or reporting violation (a required test or report was late or missed — not a measured exceedance), recorded once in January 2017. All have since returned to compliance, per EPA records.
Oakley Mutual Water Company
- Health-based Arsenic: a health-based violation (a contaminant recorded above the limit the EPA tracks), recorded 28 times between October 2021 and October 2025. The EPA record lists a level of 0.015 MG/L; the limit (MCL) is 0.01 MG/L. EPA records do not show all of these as returned to compliance.
- Health-based LEAD AND COPPER RULE REVISIONS: a health-based violation (a contaminant recorded above the limit the EPA tracks), recorded once in October 2024. The EPA record for these does not include a measured level. EPA records do not show all of these as returned to compliance.
- Monitoring LEAD AND COPPER RULE REVISIONS: a monitoring or reporting violation (a required test or report was late or missed — not a measured exceedance), recorded once in October 2024. EPA records do not show all of these as returned to compliance.
Big Oak Mobile Home Park Water
As of June 2026, EPA records show no reported violations for this system in the period covered. This is not a guarantee about every substance, or about the water inside your home's plumbing.
Knightsen Community Water System
As of June 2026, EPA records show no reported violations for this system in the period covered. This is not a guarantee about every substance, or about the water inside your home's plumbing.
Dutch Slough Water Works
- Monitoring Lead and Copper Rule: a monitoring or reporting violation (a required test or report was late or missed — not a measured exceedance), recorded 3 times between October 2017 and October 2021. EPA records do not show all of these as returned to compliance.
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.