State Well Water Guide
Washington Private Well Water Guide
Approximately 20% of Washington residents — about 1.5 million people — rely on private wells or small water systems. Well water risks divide sharply between western and eastern Washington: western Washington's high rainfall creates bacterial and turbidity risks in shallow wells, while eastern Washington's agricultural areas (Columbia Basin, Yakima Valley) have documented nitrate contamination, and the basalt geology contributes naturally occurring arsenic and fluoride. PFAS contamination has been documented near Joint Base Lewis-McChord and Fairchild AFB. Washington State has one of the more active private well programs in the country.
Testing Guidance
The Washington State Department of Health recommends annual bacteria and nitrate testing for all private wells. Arsenic testing is important for eastern Washington wells in basalt formations. PFAS testing is recommended for wells near Joint Base Lewis-McChord (Pierce County), Fairchild AFB (Spokane area), and Whidbey Island NAS. Agricultural wells in the Yakima Valley and Columbia Basin should be tested for pesticides and nitrates. Post-flood and post-earthquake testing is advised given Washington's seismic and weather activity.
What to Test For in Washington
Total coliform bacteria and E. coli — annual minimum for all wells
Nitrates — annual for Yakima Valley, Columbia Basin, and Whatcom County agricultural wells
Arsenic — eastern Washington basalt geology, particularly Grant, Adams, and Franklin counties
Fluoride — some eastern Washington formations have naturally elevated fluoride
PFAS — wells near JBLM, Fairchild AFB, and Whidbey Island NAS
Pesticides — Yakima Valley orchard and vineyard areas
Iron and manganese — widespread in western Washington wells
Turbidity — shallow wells in high-rainfall western Washington
Common Contamination Risks in Washington
Nitrate contamination in the Yakima Valley, Columbia Basin, and parts of Whatcom County from intensive agriculture
Naturally occurring arsenic in Columbia River Basalt formations across eastern Washington
PFAS contamination near Joint Base Lewis-McChord (one of the largest PFAS plumes in the Pacific Northwest)
Bacterial contamination in shallow wells during western Washington's heavy rainfall seasons
Pesticide and herbicide runoff in orchard-intensive areas of the Wenatchee and Yakima valleys
Contaminant Guides Relevant to WA Wells
Find a Certified Lab in Washington
Use the Washington state-certified laboratory program to find accredited labs for private well testing. Always verify current certification before submitting samples.
WA Certified Lab Directory ↗Washington Well Water FAQs
Related Pages
Data Sources & Provenance
All data on this page is sourced from official U.S. government or public datasets.
Quick Reference
State program
WA Certified Labs ↗EPA guidance
EPA Private Wells Program ↗State lab directory
WA Certified Labs ↗Minimum Annual Tests
Plus state-specific contaminants listed above