Here is what the EPA's own data shows about tap water in Nantucket. According to EPA SDWIS data retrieved October 2026, Nantucket is served by 2 active community water systems, together reported to serve about 30,703 people.
As of October 2026, EPA records show 13 violations across the community water system(s) serving Nantucket, going back to the earliest EPA record. 1 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.
Health-based Lead and Copper Rule: a health-based violation (a contaminant recorded above the limit the EPA tracks), recorded once in January 1996. The EPA record for these does not include a measured level. All have since returned to compliance, per EPA records.
Monitoring Consumer Confidence Rule: a monitoring or reporting violation (a required test or report was late or missed — not a measured exceedance), recorded 2 times between July 2022 and July 2025. EPA records do not show all of these as returned to compliance.
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 2008 and June 2025. 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 between July 2016 and April 2025. EPA records do not show all of these as returned to compliance.
Monitoring Nitrite: a monitoring or reporting violation (a required test or report was late or missed — not a measured exceedance), recorded once in April 2025. EPA records do not show all of these as returned to compliance.
Monitoring Public Notice: a monitoring or reporting violation (a required test or report was late or missed — not a measured exceedance), recorded once in April 2008. All have since returned to compliance, per EPA records.
Siasconset Water Department
3,000 served · groundwater · PWSID MA4197001
Monitoring Consumer Confidence Rule: a monitoring or reporting violation (a required test or report was late or missed — not a measured exceedance), recorded 2 times between July 2022 and July 2025. 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 once in April 2025. 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 October 2026. Records cover the EPA's full reporting history for these systems. Verify at EPA ECHO.