Mercury in drinking water
885 active public water systems in 43 states had a Mercury violation in the past three years, and 15 had one in the latest quarter of EPA's data.
You are on Tapcensus, an independent guide to the EPA compliance records of every public water system in the United States. This page explains Mercury and lists the water systems whose records include a related violation. It does not show measured levels.
Is Mercury in the records for your water system?
Enter a ZIP code, town, or street address to see the water systems that serve your area, their status, and which rules and contaminants appear in their violations.
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What it is and where it comes from
Inorganic mercury enters drinking water through erosion of natural deposits, discharge from refineries and factories, and runoff from landfills. Coal combustion deposits mercury in watersheds via atmospheric deposition, making it a diffuse source for surface water systems. The MCL applies to inorganic mercury; methylmercury bioaccumulation in fish is a separate concern governed by FDA.
Health effects
Chronic exposure to inorganic mercury in water primarily damages the kidneys. Neurological effects — tremors, memory loss, cognitive impairment — are more associated with organic mercury (methylmercury) than with the inorganic form regulated in drinking water. Developing fetuses and young children are most vulnerable.
The standard and what a violation means
EPA limit: 0.002 mg/L (2 ppb).
Water systems with a Mercury violation, by state
Active public water systems that reported at least one related violation to EPA in the past three years. Each state links to the list of its affected systems.
| State | Systems with violations, 3 yr | Share of active systems | In violation, latest quarter |
|---|---|---|---|
| Pennsylvania | 123 | 2% | 0 |
| Illinois | 80 | 2% | 2 |
| Texas | 73 | 1% | 0 |
| Georgia | 61 | 3% | 0 |
| New York | 58 | 1% | 0 |
| Michigan | 52 | 0% | 0 |
| New Jersey | 30 | 1% | 1 |
| Colorado | 29 | 1% | 4 |
| Indiana | 29 | 1% | 0 |
| West Virginia | 28 | 4% | 0 |
| California | 25 | 0% | 0 |
| Wyoming | 22 | 3% | 0 |
| Missouri | 21 | 1% | 2 |
| Oklahoma | 21 | 2% | 0 |
| Washington | 21 | 0% | 0 |
| Montana | 20 | 1% | 0 |
| Idaho | 19 | 1% | 1 |
| Connecticut | 18 | 1% | 0 |
| Virginia | 16 | 1% | 0 |
| Maine | 14 | 1% | 0 |
| Oregon | 13 | 1% | 0 |
| Massachusetts | 11 | 1% | 2 |
| Wisconsin | 11 | 0% | 0 |
| Utah | 10 | 1% | 0 |
| Iowa | 8 | 0% | 0 |
| Mississippi | 8 | 1% | 0 |
| Nevada | 8 | 1% | 0 |
| Alaska | 7 | 1% | 0 |
| Vermont | 7 | 1% | 2 |
| North Carolina | 6 | 0% | 0 |
| Arizona | 5 | 0% | 1 |
| Maryland | 5 | 0% | 0 |
| Minnesota | 5 | 0% | 0 |
| Alabama | 4 | 1% | 0 |
| Rhode Island | 4 | 1% | 0 |
| Florida | 3 | 0% | 0 |
| Kansas | 2 | 0% | 0 |
| New Hampshire | 2 | 0% | 0 |
| South Dakota | 2 | 0% | 0 |
| Hawaii | 1 | 1% | 0 |
| Kentucky | 1 | 0% | 0 |
| North Dakota | 1 | 0% | 0 |
| New Mexico | 1 | 0% | 0 |
Largest water systems with a Mercury violation
The ten biggest systems, by people served, whose records include a related violation in the past three years.
| System | Serves | Status | Rules violated, 3 yr | Unresolved |
|---|---|---|---|---|
|
Aqua PA Main System Montgomery County |
822,600 | 6 | 0 | |
|
Aquarion-Eastern Fairfield County Beacon Falls, Bridgeport, Darien and 17 more · Fairfield County |
351,756 | 2 | 0 | |
|
Corona, City of Corona · Riverside County |
169,380 | 6 | 0 | |
|
City of Sunnyvale Sunnyvale · Santa Clara County |
157,566 | 5 | 0 | |
|
Aqua WSC Bastrop County |
86,325 | 5 | 1 | |
|
GW Santa Cruz Water CO Maricopa · Pinal County |
84,000 | 7 | 0 | |
|
Tigard, City of Washington County |
62,500 | 2 | 0 | |
|
Elmira Water Board Elmira (c), Elmira (t), Elmira Heights (v) and 1 more · Chemung County |
54,000 | 1 | 0 | |
|
Greater Johnstown WA Riverside Cambria County |
49,500 | 7 | 0 | |
|
Greenlawn Water District Huntington (t) · Suffolk County |
42,000 | 3 | 0 |
About this data
A system is counted once if any of its violations in the past three years involved Mercury, including monitoring and reporting lapses. Rules violated and status in the systems table are for the whole system, not Mercury alone. Counts cover active systems in all 50 states and the District of Columbia.
Source: the U.S. EPA's Enforcement and Compliance History Online system (ECHO), which publishes the federal Safe Drinking Water Information System. EPA's terms and values are shown as published. The records are from EPA's data refresh of Oct 7, 2026; EPA refreshes this data quarterly, and states report to EPA with a lag of three to six months, so the newest violations may not appear yet.