Lewis County, WA
drinking water quality
87,049 residents · 167 public water systems · 21 ZIP codes
EPA sampled 2 of 167 public water systems here, together serving about 39,882 people. The highest reading was PFOS at 5.8 ng/L at Centralia Public Works - Water. 1 of the sampled system was above a federal limit. Last sampled 8/20/2024.
What was found
| Compound | Highest result | Federal limit | Ratio |
|---|---|---|---|
| PFOS | 5.8 ng/L | 4 ng/L | 1.4× |
Also detected, with no federal limit set: PFBS (4.2 ng/L).
Health-based violations
Separately from PFAS, EPA records 16 health-based violations across 12 of the county’s water systems since 2020, the most recent in 2025. They involved lead and copper, total coliform, contaminant 0700, contaminant 0300, contaminant 0200, contaminant 0800.
What this means
PFAS are industrial chemicals that EPA describes as breaking down only very slowly in the environment. In April 2024 EPA set the first enforceable national limits: 4 ng/L for PFOA and PFOS, 10 ng/L for PFHxS, PFNA and GenX.
These figures are county-level and come from EPA’s sampling of public water systems. They describe the worst result found in the county, not what comes out of any particular tap — that depends on which system serves the address, and on the plumbing in the building. A private well is not covered by this programme at all.
ZIP codes in Lewis County
98336 · 98355 · 98356 · 98361 · 98377 · 98531 · 98532 · 98533 · 98538 · 98539 · 98542 · 98544 · 98564 · 98565 · 98570 · 98572 · 98582 · 98585 · 98591 · 98593 · 98596
Readings are county-level, so every ZIP here shares the figure above. Search your ZIP on the map to see it in context.