SeaTac Water Hardness & Quality Report (2026)
Water Hardness
4.1 grains per gallon
Source
reservoir
pH Level
7.7
neutral = 7.0
Lead
0.008 mg/L
✓ Below action level
TDS
177 mg/L
Est. Daily Cost
$0.19
energy & soap waste
Source: USGS Water Quality Portal · Updated 2026
0–60
mg/L
Soft
61–120
mg/L
Moderately Hard
121–180
mg/L
Hard
180+
mg/L
Very Hard
Appliance Damage Report
In SeaTac, your appliances are currently losing 9% efficiency due to mineral buildup.
| Appliance | In SeaTac | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 7.3 yrs | 8.5 yrs | -14% |
| Washing Machine | 11 yrs | 12 yrs | -8% |
| Water Heater | 12.8 yrs | 15 yrs | -15% |
Regional Water Comparison
How SeaTac compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ SeaTac, Washington | 70.5 mg/L | 3.1 ppt | 🟡 Moderately Hard | reservoir |
| Tukwila, Washington | 46 mg/L | 2.3 ppt | 🟢 Soft | reservoir |
| Des Moines, Washington | 15 mg/L | 1.3 ppt | 🟢 Soft | reservoir |
| Burien, Washington | 53.5 mg/L | 2.5 ppt | 🟢 Soft | reservoir |
| Bryn Mawr-Skyway, Washington | 29.5 mg/L | 1.8 ppt | 🟢 Soft | reservoir |
National Benchmark
How SeaTac compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ SeaTac | 70.5 mg/L | 🟡 Low |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes SeaTac's Water Unique?
Local geology and source profile
SeaTac, Washington, in King County — a major south King County Seattle aviation hub city (SeaTac is a significant King County city — the home of Seattle-Tacoma International Airport (SEA — one of the most important aviation hubs in the Pacific Northwest and western United States; Sea-Tac Airport handles over 50 million passengers annually and is the primary gateway to Alaska and the Pacific Northwest; Sea-Tac is also a major trans-Pacific aviation hub connecting the US West Coast to East Asia); SeaTac is one of the most interesting small US cities in terms of demographics and policy history — it became nationally famous in 2013 when SeaTac voters approved a $15 per hour minimum wage (one of the first jurisdictions in the United States to pass a $15 minimum wage ordinance — the SeaTac minimum wage vote predated Seattle's $15 minimum wage by a year)), a diverse King County community with a significant East African (Ethiopian, Somali, Eritrean), Southeast Asian, and international airport service industry workforce population — draws its municipal water supply via Seattle Public Utilities. Water hardness in SeaTac measures 70.5 mg/L — classified as moderately soft.
SeaTac's moderate softness reflects the south King County Cedar River watershed's calcareous-poor Cascade Range geology. The Seattle Public Utilities distributes Cedar River supply to the south King County SeaTac zone with effective treatment, producing the moderately soft 70.5 mg/L.
With hardness at 70.5 mg/L, SeaTac residents enjoy moderately soft water. Seattle Public Utilities consistently delivers water meeting all Washington Ecology and EPA Safe Drinking Water Act requirements.
Geology & Source: River supply from the Cedar River and South Fork Tolt River watersheds via the Seattle Public Utilities — the King County south King County Seattle suburban SeaTac corridor (Precambrian calcareous-poor Cascade Range metamorphic and Quaternary calcareous-poor Cedar River glacial outwash — the calcareous-poor south King County Cedar River Seattle watershed; effective treatment); moderately soft supply at 70.5 mg/L in King County.