Metals
Selenium in U.S. tap water
249 public water systems across 21 U.S. states report Selenium in their annual Consumer Confidence Report. 1 sit at or above the federal limit.
What it is
A trace element from natural deposits and industrial discharge.
Why it's regulated
Essential in tiny amounts, but long-term exposure above the federal limit can cause hair and fingernail loss and circulatory problems.
At or above the federal limit (1)
| Water system | Measured | vs. limit |
|---|---|---|
| Mendota, City of — Mendota, Ca, CA 2023 annual report | 5–50 ug/L | 1.0× the limit |
Approaching the limit (2)
| Water system | Measured | vs. limit |
|---|---|---|
| Slocsa #10a - Cayucos — San Luis Obispo, Ca, CA 2023 annual report | 48 ug/L | 1.0× the limit |
| Golden State Water Company - Simi Valley — Rancho Cordova, Ca, CA 2023 annual report | 45 ug/L | 0.9× the limit |
Within the federal limit (246)
Showing 50 of 246. The full list is in the JSON API.
Selenium by state
Every state where a public water system reports Selenium in its annual report, ranked by systems at or above the federal limit.
Frequently asked
+What is Selenium?
A trace element from natural deposits and industrial discharge. Essential in tiny amounts, but long-term exposure above the federal limit can cause hair and fingernail loss and circulatory problems.
+What is the federal limit for Selenium in drinking water?
The federal MCL for Selenium is 0.05 mg/L. The EPA enforces this against the regulated reporting statistic (typically a running annual average or 90th percentile), not a single-sample spike.
+How many U.S. water systems have Selenium over the federal limit?
1 of the 249 public water systems on The Water Map report Selenium at or above its federal limit, spanning 21 U.S. states. The full list is on this page.
+Which states report the most Selenium in their drinking water?
Of the systems on The Water Map, California (1 system at or above the limit) report the most Selenium exceedances. The state-by-state table on this page lists every state.
+How can I check if Selenium is in my city's tap water?
Search your city on The Water Map (https://www.thewatermap.com/) or browse the list on this page. Every U.S. public water utility is required to publish an annual Consumer Confidence Report that lists every contaminant it measured, including Selenium.