At elevated levels, Arsenic is a recognized health concern in drinking water; in Seattle, Washington, it has been detected in recent samples logged through federal compliance reporting.

Data: EPA SDWIS, CCR Reports, ECHO Last verified: 2026-05-14

Arsenic in Seattle Tap Water

Arsenic has been detected in Seattle, Washington drinking water at a maximum level of 400 ppb — 40x the EPA MCL.

This analysis covers 1,160,710 residents across 62 ZIP codes in Seattle.

Seattle's overall water quality grade is A (95/100).

Is Arsenic in Seattle Water Safe?

If you live in an affected ZIP code, consider installing a reverse osmosis filter certified under NSF 53 / NSF 58 and testing your water independently.

Arsenic Levels by ZIP Code

Average arsenic level across Seattle: 400 ppb

Health Effects of Arsenic

• Increased risk of skin, bladder, lung, and kidney cancer
• Cardiovascular disease and type 2 diabetes
• Skin changes (darkening, thickening, lesions)
• Developmental effects in children exposed in utero

Health risk severity: High. Governed by the Arsenic Rule (2006).

How Arsenic Gets Into Drinking Water

• Natural deposits in rock and soil (especially in western U.S.)
• Runoff from orchards and glass/electronics production
• Historical use of arsenic-based pesticides
• Well water in areas with arsenic-rich geology

What to Do About Arsenic in Seattle Water

1. Install a reverse osmosis (RO) system certified under NSF 58
2. Adsorptive media filters (iron-based) can also reduce arsenic
3. Have well water tested if on a private supply
4. Boiling water does NOT remove arsenic — it concentrates it

Look for filters certified under NSF 53 / NSF 58 for arsenic removal.

Related

• Arsenic — National Overview
• Arsenic in Washington
• Washington Water Quality
• Seattle Water Quality
• Check Your ZIP Code