Cyanide in drinking water
793 active public water systems in 38 states had a Cyanide violation in the past three years, and 8 have one that is still unresolved.
You are on Tapcensus, an independent guide to the EPA compliance records of every public water system in the United States. This page explains Cyanide and lists the water systems whose records include a related violation. It does not show measured levels.
Is Cyanide 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
Cyanide in drinking water originates primarily from industrial discharges — metal plating, steel manufacturing, and certain mining operations — and from leaching of road salt formulations that contain ferrocyanide compounds. It can also enter from improper disposal of industrial waste. Natural background levels are negligible. It is measured as free cyanide.
Health effects
Acute high-dose cyanide exposure interferes with cellular oxygen use and can cause rapid deterioration of the central nervous system, including headache, dizziness, and in severe cases, loss of consciousness. Chronic exposure at lower levels is associated with thyroid dysfunction and nerve damage. Most drinking water violations pose chronic rather than acute risk.
The standard and what a violation means
EPA limit: 0.2 mg/L (200 ppb).
Water systems with a Cyanide 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 | Unresolved |
|---|---|---|---|
| Pennsylvania | 138 | 2% | 0 |
| Texas | 104 | 1% | 0 |
| Illinois | 67 | 1% | 2 |
| Georgia | 61 | 3% | 0 |
| New York | 56 | 1% | 0 |
| Michigan | 40 | 0% | 0 |
| New Jersey | 35 | 1% | 0 |
| Indiana | 29 | 1% | 0 |
| West Virginia | 27 | 4% | 0 |
| Wyoming | 23 | 3% | 0 |
| Connecticut | 21 | 1% | 0 |
| Washington | 21 | 0% | 0 |
| Oregon | 13 | 1% | 0 |
| Minnesota | 12 | 0% | 0 |
| Missouri | 11 | 0% | 1 |
| Iowa | 10 | 1% | 1 |
| Massachusetts | 10 | 1% | 2 |
| Mississippi | 10 | 1% | 0 |
| Nevada | 10 | 2% | 0 |
| Oklahoma | 10 | 1% | 0 |
| Utah | 10 | 1% | 0 |
| Vermont | 10 | 1% | 1 |
| Montana | 9 | 0% | 0 |
| Maine | 8 | 0% | 0 |
| Alaska | 6 | 0% | 0 |
| Arizona | 6 | 0% | 1 |
| California | 6 | 0% | 0 |
| North Carolina | 6 | 0% | 0 |
| Alabama | 4 | 1% | 0 |
| Wisconsin | 4 | 0% | 0 |
| Florida | 3 | 0% | 0 |
| Rhode Island | 3 | 1% | 0 |
| Virginia | 3 | 0% | 0 |
| Idaho | 2 | 0% | 0 |
| South Dakota | 2 | 0% | 0 |
| Kentucky | 1 | 0% | 0 |
| North Dakota | 1 | 0% | 0 |
| Nebraska | 1 | 0% | 0 |
Largest water systems with a Cyanide 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 | |
|
Atlantic City Mua Atlantic City · Atlantic County |
152,415 | 3 | 0 | |
|
Aqua WSC Bastrop County |
86,325 | 5 | 1 | |
|
GW Santa Cruz Water CO Maricopa · Pinal County |
84,000 | 7 | 0 | |
|
State College Boro Water Auth Centre County |
72,000 | 5 | 0 | |
|
Johnson County SUD Johnson County |
65,517 | 2 | 0 | |
|
Tigard, City of Washington County |
62,500 | 2 | 0 | |
|
Perth Amboy Water Department Perth Amboy City · Middlesex County |
52,328 | 2 | 0 | |
|
City of Sherman Grayson County |
43,645 | 2 | 0 |
About this data
A system is counted once if any of its violations in the past three years involved Cyanide, including monitoring and reporting lapses. Rules violated and status in the systems table are for the whole system, not Cyanide 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.