Mercury in U.S. Drinking Water
Health-based violation data for Mercury from EPA Safe Drinking Water Information System (SDWIS). Covers all community water systems with violations on record.
Mercury has been found in violation of EPA standards in 108 water systems across 8 states, with 479 total health-based violations recorded. The most affected states are New York, California, Pennsylvania.
Mercury is regulated under the EPA Safe Drinking Water Act, which sets enforceable Maximum Contaminant Levels (MCLs) and associated treatment technique requirements for public water systems. The EPA Safe Drinking Water Information System (SDWIS) tracks every recorded violation nationwide and links it back to the specific public water system (PWSID), violation type, and begin date.
Across the United States, SDWIS records show 479 health-based violations for Mercury affecting 108 community water systems in 8 states. Violation counts cluster heaviest in New York, California, Pennsylvania, with New York alone accounting for 140 violations across 36 systems. The contaminant is listed on the federal primary drinking water regulations.
A health-based violation does not mean residents were necessarily harmed, it means the contaminant exceeded the federal MCL in a compliance sample, triggering notification and remediation requirements. States and utilities maintain primary enforcement responsibility. To check the status of a specific water system, request its most recent Consumer Confidence Report or consult the EPA's Drinking Water Watch portal for the corresponding state.
Violations by State
States ranked by number of health-based violations for Mercury.
| # | State | Violations | Systems Affected |
|---|---|---|---|
| 1 | New York | 140 | 36 |
| 2 | California | 63 | 13 |
| 3 | Pennsylvania | 10 | 1 |
| 4 | Delaware | 8 | 5 |
| 5 | Connecticut | 4 | 1 |
| 6 | Illinois | 4 | 2 |
| 7 | New Mexico | 1 | 1 |
| 8 | Ohio | 1 | 1 |
Most Affected Water Systems
Top 50 water systems by number of Mercury health-based violations.
Frequently Asked Questions
Is Mercury in my water?
Mercury has been detected in violation of EPA health standards in 108 water systems across 8 states. To check your specific utility, look up your annual Consumer Confidence Report (CCR) - water systems are required to disclose all violations.
How many water systems have Mercury violations?
EPA SDWIS records show 108 community water systems with health-based Mercury violations, totaling 479 violations. These represent cases where the contaminant exceeded the EPA Maximum Contaminant Level (MCL).
Which states have the most Mercury violations?
The states with the most Mercury violations are: New York (140 violations), California (63 violations), Pennsylvania (10 violations), Delaware (8 violations), Connecticut (4 violations).
Explore More
About This Data
Violation data is from the EPA Safe Drinking Water Information System (SDWIS). Only health-based violations are shown, these include Maximum Contaminant Level (MCL) and Treatment Technique (TT) violations. Monitoring and reporting violations are excluded. Data may not reflect the most current enforcement actions.
Source: U.S. Environmental Protection Agency, SDWIS Federal Reporting Services U.S. Environmental Protection Agency, SDWIS Federal Reporting Services
Read our methodology - how this data is sourced, computed, and verified.