Selenium in drinking water
861 active public water systems in 44 states had a Selenium violation in the past three years, and 21 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 Selenium and lists the water systems whose records include a related violation. It does not show measured levels.
Is Selenium 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.
Enter a ZIP code, town, or street address.
What it is and where it comes from
Selenium is a naturally occurring metalloid present in certain soils and rock formations. It enters drinking water through weathering of seleniferous soils and rock, agricultural irrigation return flows, and discharge from petroleum refineries and metal smelters. Selenium is an essential trace nutrient at low concentrations but is toxic at levels above the MCL.
Health effects
Chronic exposure above the MCL causes selenosis — characterized by hair and nail loss, peripheral neuropathy, fatigue, and gastrointestinal disturbance. Liver damage can occur with prolonged high intake. The margin between nutritional requirement and toxic dose is narrow, making the MCL an important threshold.
The standard and what a violation means
EPA limit: 0.05 mg/L (50 ppb).
Water systems with a Selenium 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 | 116 | 2% | 0 |
| Texas | 76 | 1% | 3 |
| Illinois | 69 | 1% | 2 |
| Georgia | 61 | 3% | 0 |
| New York | 54 | 1% | 0 |
| Michigan | 48 | 0% | 0 |
| West Virginia | 31 | 4% | 0 |
| Colorado | 30 | 1% | 4 |
| California | 29 | 0% | 3 |
| Indiana | 29 | 1% | 0 |
| New Jersey | 27 | 1% | 0 |
| Wyoming | 22 | 3% | 0 |
| Missouri | 21 | 1% | 2 |
| Washington | 21 | 0% | 0 |
| Montana | 20 | 1% | 0 |
| Oklahoma | 20 | 2% | 0 |
| Idaho | 19 | 1% | 1 |
| Connecticut | 17 | 1% | 0 |
| Virginia | 15 | 1% | 0 |
| Oregon | 13 | 1% | 0 |
| Maine | 12 | 1% | 0 |
| Wisconsin | 11 | 0% | 0 |
| Massachusetts | 10 | 1% | 2 |
| Utah | 10 | 1% | 0 |
| Iowa | 8 | 0% | 0 |
| Nevada | 8 | 1% | 0 |
| Alaska | 7 | 1% | 0 |
| Mississippi | 7 | 1% | 0 |
| Vermont | 7 | 1% | 2 |
| Arizona | 6 | 0% | 2 |
| North Carolina | 6 | 0% | 0 |
| Maryland | 5 | 0% | 0 |
| Minnesota | 5 | 0% | 0 |
| Alabama | 4 | 1% | 0 |
| Kansas | 3 | 0% | 0 |
| Rhode Island | 3 | 1% | 0 |
| Florida | 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 |
| Nebraska | 1 | 0% | 0 |
| New Mexico | 1 | 0% | 0 |
Largest water systems with a Selenium 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 | |
|
Greenlawn Water District Huntington (t) · Suffolk County |
42,000 | 3 | 0 | |
|
Winslow Twp Dmu Winslow Twp · Camden County |
39,174 | 6 | 0 | |
|
Jackson Twp Mua Jackson Twp · Ocean County |
37,224 | 3 | 0 |
About this data
A system is counted once if any of its violations in the past three years involved Selenium, including monitoring and reporting lapses. Rules violated and status in the systems table are for the whole system, not Selenium 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.