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.
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.
+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.