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Updated 2026-10-15
County water report

King County Water Quality: 14 Cities Ranked by the Records

King County, Washington: 14 city reports built from EPA and utility records. A county has many suppliers; each city shows the system that serves it.

Find my systemOpen on the mapPrivate wells in King County
Across the county's systems

Highest result for each contaminant

One row per contaminant: the highest result any system in the county reported, against its limit. Open a row for the systems behind it.

Perfluorooctanesulfonic acid (PFOS)Detected in 3 systems of 14 tested4.0 ng/L federal MCL (2024) · US EPAHighest11.1 ng/L
Perfluorohexanesulfonic acid (PFHxS)Detected in 2 systems of 14 tested10 ng/L federal MCL (2024) · US EPAHighest16.5 ng/L
LithiumDetected in 1 system of 14 tested10 µg/L EPA health reference level (screening, not a legal limit) · US EPAHighest13 µg/L
  • REDMOND WATER SYSTEM CITY OF13 µg/LSample date: 2023-11-06 to 2024-08-14
  • Auburn City ofNot detected · below 9.0 µg/L lab reporting limitSample date: 2024-11-06 to 2025-11-19
  • BELLEVUE CITY OFNot detected · below 9.0 µg/L lab reporting limitSample date: 2024-01-09 to 2024-10-08
  • DUVALL CITY OFNot detected · below 9.0 µg/L lab reporting limitSample date: 2023-06-12 to 2024-03-04
  • ENUMCLAW WATER DEPARTMENTNot detected · below 9.0 µg/L lab reporting limitSample date: 2023-03-14 to 2023-09-26
  • ISSAQUAH WATER SYSTEMNot detected · below 9.0 µg/L lab reporting limitSample date: 2024-09-04 to 2025-06-12
  • KENT WATER DEPARTMENTNot detected · below 9.0 µg/L lab reporting limitSample date: 2025-01-27 to 2025-12-04
  • KIRKLAND CITY OFNot detected · below 9.0 µg/L lab reporting limitSample date: 2024-09-11 to 2025-06-03
  • LAKEHAVEN WATER AND SEWER DISTRICTNot detected · below 9.0 µg/L lab reporting limitSample date: 2024-07-17 to 2025-03-04
  • MERCER ISLAND CITY OFNot detected · below 9.0 µg/L lab reporting limitSample date: 2023-09-12 to 2024-06-11
  • RENTON CITY OFNot detected · below 9.0 µg/L lab reporting limitSample date: 2023-03-23 to 2023-09-20
  • SAMMAMISH PLATEAU WATER & SEWERNot detected · below 9.0 µg/L lab reporting limitSample date: 2023-05-15 to 2024-02-12
  • SEATTLE PUBLIC UTILITIESNot detected · below 9.0 µg/L lab reporting limitSample date: 2023-03-14 to 2023-12-18
  • SNOQUALMIE WATERNot detected · below 9.0 µg/L lab reporting limitSample date: 2023-01-25 to 2023-10-11
Haloacetic acids (HAA5)Detected in 2 systems60 ppb federal MCL · US EPAHighest28 ppb
Total trihalomethanes (TTHM)Detected in 2 systems80 ppb federal MCL · US EPAHighest34 ppb
Lead (90th percentile)Detected in 9 systems of 10 tested15 µg/L federal action level · US EPAHighest3.3 µg/L
Perfluorobutanesulfonic acid (PFBS)Detected in 6 systems of 14 tested2,000 ng/L EPA health advisory (screening, not a legal limit) · US EPAHighest8.8 ng/L
Perfluorohexanoic acid (PFHxA)Detected in 2 systems of 14 tested400,000 ng/L Michigan EGLE state MCL (strictest US state) · Michigan EGLEHighest7.6 ng/L
4 more contaminants detectedShow
Water hardnessDetected in 5 systemsAesthetic, no federal health limit · USGSHighest5 gpg
Perfluoroheptanoic acid (PFHpA)Detected in 1 system of 14 testedNo federal or state limit; shown for transparencyHighest3.6 ng/L
Perfluoropentanesulfonic acid (PFPeS)Detected in 1 system of 14 testedNo federal or state limit; shown for transparencyHighest4.1 ng/L
Perfluoropentanoic acid (PFPeA)Detected in 2 systems of 14 testedNo federal or state limit; shown for transparencyHighest13.7 ng/L
22 PFAS tested, none detected in any systemShow

Tested in these 14 systems: Auburn City of, BELLEVUE CITY OF, DUVALL CITY OF, ENUMCLAW WATER DEPARTMENT, ISSAQUAH WATER SYSTEM, KENT WATER DEPARTMENT, KIRKLAND CITY OF, LAKEHAVEN WATER AND SEWER DISTRICT, MERCER ISLAND CITY OF, REDMOND WATER SYSTEM CITY OF, RENTON CITY OF, SAMMAMISH PLATEAU WATER & SEWER, SEATTLE PUBLIC UTILITIES, SNOQUALMIE WATER

  • 11-Chloroeicosafluoro-3-oxaundecane-1-sulfonic acid (11Cl-PF3OUdS)
  • 1H, 1H, 2H, 2H-perfluorodecane sulfonic acid (8:2 FTS)
  • 1H, 1H, 2H, 2H-perfluorohexane sulfonic acid (4:2 FTS)
  • 1H, 1H, 2H, 2H-perfluorooctane sulfonic acid (6:2 FTS)
  • 4,8-Dioxa-3H-perfluorononanoic acid (ADONA)
  • 9-Chlorohexadecafluoro-3-oxanone-1-sulfonic acid (9Cl-PF3ONS)
  • Hexafluoropropylene oxide dimer acid (HFPO-DA) (GenX chemicals)
  • N-ethyl perfluorooctanesulfonamidoacetic acid (NEtFOSAA)
  • N-methyl perfluorooctanesulfonamidoacetic acid (NMeFOSAA)
  • Nonafluoro-3,6-dioxaheptanoic acid (NFDHA)
  • Perfluoro (2-ethoxyethane) sulfonic acid (PFEESA)
  • Perfluoro-3-methoxypropanoic acid (PFMPA)
  • Perfluoro-4-methoxybutanoic acid (PFMBA)
  • Perfluorobutanoic acid (PFBA)
  • Perfluorodecanoic acid (PFDA)
  • Perfluorododecanoic acid (PFDoA)
  • Perfluoroheptanesulfonic acid (PFHpS)
  • Perfluorononanoic acid (PFNA)
  • Perfluorooctanoic acid (PFOA)
  • Perfluorotetradecanoic acid (PFTA)
  • Perfluorotridecanoic acid (PFTrDA)
  • Perfluoroundecanoic acid (PFUnA)
14 cities

Cities ranked by the records

Showing 6 of 14 cities · scores are system-level, not tap tests

Ranked by the Purity Score of each city's main water system, highest first. Scores belong to water systems; there is no county score. The score is computed only from contaminants measured in the published EPA record, so this ranks the record, not which city's water is safest. How the score works.

PFAS in King County3 of 14 city reports had a PFAS sample above a 2024 EPA limit
  1. Sammamish11.1 ng/L
  2. Redmond5 ng/L
  3. Federal Way4.1 ng/L
4.0 ng/L federal MCL · PFOS, ng/LPFAS in Washington
Lead

0of 14 cities above the 15 µg/L action level

Based on each system's 90th-percentile result. Lead from household plumbing isn't in this record.

Lead in Washington
Hard water

5cities report hardness · hardest Kent, 5 gpg

None above 7 gpg, the USGS threshold for hard water. An aesthetic measure with no federal health limit.

Hard water explained
Who supplies the county

Largest water systems

  1. SeattleSEATTLE PUBLIC UTILITIES · WA5377050
    1,161,961 served
  2. BellevueBELLEVUE CITY OF · WA5305575
    321,349 served
  3. KentKENT WATER DEPARTMENT · WA5338150
    166,421 served
  4. RedmondREDMOND WATER SYSTEM CITY OF · WA5371650
    163,335 served
  5. Federal WayLAKEHAVEN WATER AND SEWER DISTRICT · WA5341997
    148,809 served
  6. RentonRENTON CITY OF · WA5371850
    108,091 served
  7. AuburnAuburn City of · WA5303350
    107,655 served
  8. SammamishSAMMAMISH PLATEAU WATER & SEWER · WA5340900
    79,362 served
  9. KirklandKIRKLAND CITY OF · WA5342250
    69,243 served
  10. IssaquahISSAQUAH WATER SYSTEM · WA5336350
    43,584 served
Questions

Frequently asked

How does King County tap water compare across cities?

PurityMap ranks 14 cities in King County by the Purity Score of each city's main water system, computed only from contaminants measured in the published EPA record. Scores belong to water systems, not to cities. The highest published score is Bellevue's main water system: BELLEVUE CITY OF · PWSID WA5305575 · Purity Score 100 (Excellent) · Confidence: low · Assessed at the water-system level. The ranking compares the records, not which city's water is safest, and your own tap can differ with household plumbing.

How many King County cities had a PFAS sample above a 2024 EPA limit?

3 of 14 King County city reports had a PFAS sample above a 2024 EPA limit in EPA's UCMR 5 testing, including Sammamish (PFOS 11.1 ng/L), Redmond (PFOS 5 ng/L), Federal Way (PFOS 4.1 ng/L). That limit is judged on a yearly average, and water systems have until 2029 to meet it, so a single sample is not a violation. PFAS were detected at any level in 6.

Is there lead in King County tap water?

Utilities report lead as a 90th-percentile result from home taps. 9 of 14 King County cities reported a value above zero, and none was above the 15 µg/L federal action level. Lead usually comes from a building's own pipes and fixtures, so only a test at your tap tells you what you drink.

Does King County have hard water?

Hardness is published in utility water-quality reports for 5 King County cities on record; the hardest is Kent at 5 grains per gallon. Hardness affects scale and appliances; it is not a health finding.

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