Water Quality Report · Updated October 07, 2026
SAMMAMISH PLATEAU WATER & SEWER
SAMMAMISH PLATEAU WATER & SEWER delivers tap water graded D (56/100) by TapWaterSafety.org. The utility serves approximately 79,362 residents in Sammamish, Washington using surface water (purchased). The most significant water quality concerns are: PFAS contamination; Perfluorohexane sulfonate (PFHXS) significantly above health guideline; Total PFOS and PFOA significantly above health guideline; Haloacetic acids (HAA9) significantly above health guideline.
Is Sammamish tap water safe to drink?
SAMMAMISH PLATEAU WATER & SEWER delivers tap water that earns a grade of D (56/100) from TapWaterSafety.org — a below-average rating, with multiple concerns including pfas contamination.
The utility serves 79,362 residents in Sammamish, drawing from surface water (purchased).
Public testing data identifies 18 contaminants in this water above EWG's health-based guidelines, including: Perfluorooctane sulfonate (PFOS), Perfluorohexane sulfonate (PFHXS), Total PFOS and PFOA, Haloacetic acids (HAA9), Haloacetic acids (HAA5), Total trihalomethanes (TTHMs), Perfluorononanoic acid (PFNA), Trichloroacetic acid, Chloroform, Bromodichloromethane, Dichloroacetic acid, Bromochloroacetic acid, Dibromochloromethane, Perfluorooctanoic acid (PFOA), Chromium (hexavalent), Nitrate, Nitrate and nitrite, Perfluoropentane sulfonic acid (PFPeS). For most residents, a properly certified home filter at the kitchen tap is the most cost-effective way to reduce exposure to whatever's in your water. See our filter recommendations below, matched specifically to this utility's contaminant profile.
EPA compliance record
Official U.S. EPA records for SAMMAMISH PLATEAU WATER & SEWER (system ID WA5340900) for the last 3 years. Checked 2026-10-07.
Source: U.S. EPA Enforcement and Compliance History Online (ECHO), from the Safe Drinking Water Information System. See EPA's full report.
Quick actions for Sammamish residents
Top concerns in this water
Based on the most recent EPA and EWG data, these are the most significant water quality issues for SAMMAMISH PLATEAU WATER & SEWER.
PFAS contamination
Severe concernPerfluorononanoic acid (PFNA), Perfluorooctane sulfonate (PFOS) detected. PFAS are persistent chemicals linked to cancer and immune effects with no known safe exposure threshold.
Perfluorohexane sulfonate (PFHXS) significantly above health guideline
Moderate concernPerfluorohexane sulfonate (PFHXS) detected at 8.19 ppt, 8189x above the EWG health guideline of 0.001 ppt.
Total PFOS and PFOA significantly above health guideline
Moderate concernTotal PFOS and PFOA detected at 12.4 ppt, 1770x above the EWG health guideline of 0.007 ppt.
Haloacetic acids (HAA9) significantly above health guideline
Moderate concernHaloacetic acids (HAA9) detected at 14.4 ppb, 240x above the EWG health guideline of 0.06 ppb.
Contact SAMMAMISH PLATEAU WATER & SEWER
Reach the utility directly for service issues, water quality concerns, or to request your Consumer Confidence Report.
General Contact
Treatment Plant
Recommended water filters for Sammamish
Filters matched to the specific contaminants in this water supply.
Filter certified for PFOA/PFOS (NSF/ANSI 53 or 58)
$180-$750Reverse osmosis and some carbon block filters reduce PFAS. Look for certification to NSF/ANSI 53 or 58 for PFOA/PFOS.
Carbon filter certified for VOCs (NSF/ANSI 53)
$180-$599Activated carbon is effective for disinfection byproducts. Look for NSF/ANSI 53 VOC reduction.
Disclosure: TapWaterSafety earns a commission from purchases made through these links. This does not influence our scoring methodology or filter selection.
Score breakdown
This utility's overall score of 56/100 breaks down across five weighted components. Read the full methodology →
Contaminants detected — international standards comparison
Every contaminant detected, compared side-by-side against US EPA legal limits, the EU Drinking Water Directive (2020/2184), WHO Guidelines, and California's Public Health Goal (the strictest US benchmark). Why we show multiple standards →
| Contaminant | Detected | EWG US health-based |
EPA US legal |
EU DWD Europe |
WHO global |
CA PHG strictest US |
Tested sample year |
Status |
|---|---|---|---|---|---|---|---|---|
| Perfluorooctane sulfonate (PFOS) PFAS |
5.79 ppt | 0.3 | 4.0 | 100 | 100 | 1 | — | EPA violation |
| Perfluorohexane sulfonate (PFHXS) PFAS |
8.19 ppt | 0.001 | 10.0 | — | — | — | — | 8189× over |
| Total PFOS and PFOA PFAS |
12.4 ppt | 0.007 | — | 100 | 100 | 0.007 | — | 1770× over |
| Haloacetic acids (HAA9) Disinfection byproduct |
14.4 ppb | 0.06 | — | — | — | — | — | 240× over |
| Haloacetic acids (HAA5) Disinfection byproduct |
13.7 ppb | 0.1 | 60.0 | 60 | — | — | — | 137× over |
| Total trihalomethanes (TTHMs) Disinfection byproduct |
17.8 ppb | 0.15 | 80.0 | 100 | — | — | — | 118× over |
| Perfluorononanoic acid (PFNA) PFAS |
0.582 ppt | 0.006 | 10.0 | — | — | — | — | 97× over |
| Trichloroacetic acid Disinfection byproduct |
7.36 ppb | 0.1 | — | — | — | — | — | 74× over |
| Chloroform Disinfection byproduct |
14.8 ppb | 0.4 | — | — | — | — | — | 37× over |
| Bromodichloromethane Disinfection byproduct |
2.16 ppb | 0.06 | — | — | — | — | — | 36× over |
| Dichloroacetic acid Disinfection byproduct |
5.99 ppb | 0.2 | — | — | — | — | — | 30× over |
| Bromochloroacetic acid Disinfection byproduct |
0.197 ppb | 0.02 | — | — | — | — | — | 9.9× over |
| Dibromochloromethane Disinfection byproduct |
0.578 ppb | 0.1 | — | — | — | — | — | 5.8× over |
| Perfluorooctanoic acid (PFOA) PFAS |
0.514 ppt | 0.09 | 4.0 | 100 | 100 | 0.007 | — | 5.7× over |
| Chromium (hexavalent) Heavy metal |
0.109 ppb | 0.02 | — | — | — | — | — | 5.5× over |
| Nitrate Inorganic |
0.651 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 4.7× over |
| Nitrate and nitrite Inorganic |
0.593 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 4.2× over |
| Perfluoropentane sulfonic acid (PFPeS) PFAS |
1.34 ppt | 1.0 | — | — | — | — | — | 1.3× over |
| Dibromoacetic acid Disinfection byproduct |
0.0205 ppb | 0.03 | — | — | — | — | — | Below guideline |
| Chlorate Disinfection byproduct |
78.9 ppb | 210.0 | — | — | — | — | — | Below guideline |
| Manganese Heavy metal |
11.4 ppb | 100.0 | — | 50 | 80 | — | — | Below guideline |
| Vanadium Other |
1.03 ppb | 21.0 | — | — | — | — | — | Below guideline |
| Bromoform Disinfection byproduct |
0.00664 ppb | 0.5 | — | — | — | — | — | Below guideline |
| Monochloroacetic acid Disinfection byproduct |
0.334 ppb | 53.0 | — | — | — | — | — | Below guideline |
| Perfluorobutane sulfonate (PFBS) PFAS |
3.71 ppt | 2000.0 | — | — | — | — | — | Below guideline |
| Perfluoropentanoic Acid (PFPeA) PFAS |
1.15 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Perfluorohexanoic Acid (PFHxA) PFAS |
1.11 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Perfluorobutanoic Acid (PFBA) PFAS |
0.227 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Strontium Radiological |
0.0984 ppb | 1500.0 | — | — | — | — | — | Below guideline |
| Fluoride Inorganic |
0.138 ppm | — | 4.0 | 1.5 | 1.5 | — | — | Below guideline |
| PFOS + PFOA + PFHxS + PFNA PFAS |
27.5 ppt | — | — | 100 | 100 | 0.007 | — | Below guideline |
All values in the unit of the detected level. Red cells indicate the detected level exceeds that standard. Some contaminants have limits in some jurisdictions but not others (shown as —). The "Tested" column shows the year each contaminant sample was collected.
Sources: US EPA, EU Drinking Water Directive 2020/2184, WHO Guidelines (4th ed.), California OEHHA PHGs, EWG Tap Water Database.
SAMMAMISH PLATEAU WATER & SEWER service area
This water system serves 1 community in King County, Washington. Click any city for its dedicated tap water quality page.
Find the right filter for Sammamish water
Browse filter categories by water-quality concern. Each option below is NSF-certified for the matched contaminant type.