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.
- View Arsenic Detections in Washington Public Water Supplies Map
- Arsenic Treatment Optimization Program (PDF)
Publications and Webpages
Resources
- Financial Assistance information is available on our Drinking Water State Revolving Fund (DWSRF) page.
External Resources
- Environmental Protection Agency (EPA)
- EPA Arsenic Rule Compliance for Community Water System Owners and Operators
- Department of Ecology Common Cleanup Situations for Homeowners and Small Businesses
- Department of Ecology Health Effects of Arsenic and Lead
- U.S. Geological Survey—Mapping Arsenic in Groundwater
Staff Contact Information
Go to our Contacts and Office Location page where you'll find our org chart, program email addresses, an interactive map with county assignments, a link to our Staff Directory, and more. For drinking water and statewide source monitoring questions, use the interactive map and call the ODW staff assigned to your county.