Selenium in Drinking Water: Complete Guide (2026)

What is Selenium and Why Does It Matter?

# Selenium in Drinking Water: What You Need to Know

Selenium is a naturally occurring element found in soil and rock. It enters your tap water when groundwater passes through selenium-rich geological formations, particularly in the western United States and the Great Plains. Coal burning, oil refining, and metal smelting also release selenium into the environment. Unlike some contaminants that are purely man-made, selenium exists in nature—but human activities have increased the amount reaching drinking water supplies. When selenium concentrations get too high, they become a health concern.

Our analysis found selenium in 6,008 water systems across the country, with 54 systems exceeding safe drinking guidelines. The average selenium level was 3.72 ppb (parts per billion), but some systems tested as high as 146.8 ppb—nearly 30 times the EPA's legal limit of 5 ppb. This variation matters. Most people drinking selenium-containing water face minimal risk at current levels, but those in affected areas should know what they're exposed to.

At low levels, selenium is actually essential for human health. Your body needs it for thyroid function and antioxidant protection. The EPA set the drinking water limit at 5 ppb based on studies showing that higher chronic exposure can cause selenosis—a condition involving hair and nail brittleness, skin rashes, and nervous system damage. The Environmental Working Group (EWG) recommends a stricter guideline of 0.15 ppb for maximum protection, especially for pregnant women and children whose developing bodies are more vulnerable. Between the EPA limit and the EWG guideline lies a gray zone where risk increases but isn't immediate.

Texas leads the nation with selenium detections in 958 water systems, followed by Kansas (662), California (512), Illinois (443), and Colorado (420). This geographic pattern reflects geology. Texas and Kansas sit atop the Ogallala Aquifer, a massive underground water source with naturally high selenium concentrations. California's Central Valley and Colorado's agricultural regions also have selenium-rich soil. These aren't failures of water treatment—they're the result of where water naturally flows through selenium-bearing rock layers. Communities in these states should prioritize testing and treatment more urgently than those in areas with naturally low selenium.

If your water system shows elevated selenium, several proven removal methods work effectively. Reverse osmosis systems remove up to 99.9% of selenium, making them one of the most reliable options for home use. Ion exchange resins also capture selenium effectively, though they require regular maintenance. Activated carbon filters alone won't remove selenium, so don't rely on basic pitcher filters if you're in a high-selenium area. The best approach: request a water quality report from your local utility (they're required to provide one), check if selenium appears on it, and if it does, invest in a certified system. Point-of-use filters installed at your kitchen sink are practical for drinking and cooking water. Whole-house systems work if you're concerned about selenium in all water uses, though selenium exposure through bathing is minimal compared to ingestion.

Start by knowing your numbers. Contact your water provider and ask for their latest water quality report. If selenium appears above 5 ppb, or if you live in Texas, Kansas, California, Illinois, or Colorado and want extra assurance, testing your tap water directly gives you certainty. Echo Water's testing services can identify selenium levels in your specific home, accounting for how your plumbing might affect results. From there, choosing the right filter becomes straightforward—and your family gets the protection you're looking for.

Regulatory Standards for Selenium

Cities With the Highest Selenium Levels

States Most Affected by Selenium

Frequently Asked Questions

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