Arsenic in Drinking Water

Arsenic and Where it Comes From

Arsenic occurs naturally in the earth's crust. Most arsenic in drinking water comes from natural rock formations. As water flows through these formations, it can dissolve arsenic and carry it into underground aquifers, streams, or rivers that may become drinking water supplies. Arsenic can also come from human activities, such as mining or smelting ores that contain arsenic. In the past, it was used in commercial wood preservatives and agricultural chemicals.

Drinking Water Standard for Arsenic

For many years, the drinking water standard for arsenic was 50 parts per billion (ppb). The U.S. Environmental Protection Agency (EPA) tightened the standard from 50 ppb to 10 ppb in January 2001 for federally regulated (Group A) community and non-transient non-community (NTNC) water systems. EPA changed the arsenic standard to reduce people's long-term exposure to arsenic in drinking water, which has been linked to chronic health issues.

Washington State adopted the revised arsenic standard January 14, 2004.

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External Resources

Regional Offices

For drinking water and statewide source monitoring questions, call the regional office nearest you.

Eastern Regional Office 509-329-2100

Northwest Regional Office 253-395-6750

Southwest Regional Office 360-236-3030