Issaquah Water Hardness & Quality Report (2026)
Water Hardness
2.6 grains per gallon
Source
reservoir
pH Level
7.4
neutral = 7.0
Lead
0.005 mg/L
✓ Below action level
TDS
90 mg/L
Est. Daily Cost
$0.12
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 Issaquah, your appliances are currently losing 6% efficiency due to mineral buildup.
| Appliance | In Issaquah | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 8.1 yrs | 8.5 yrs | -5% |
| Washing Machine | 12 yrs | 12 yrs | — |
| Water Heater | 13.8 yrs | 15 yrs | -8% |
Regional Water Comparison
How Issaquah compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ Issaquah, Washington | 44 mg/L | 2.2 ppt | 🟢 Soft | reservoir |
| City of Sammamish, Washington | 59.5 mg/L | 2.7 ppt | 🟢 Soft | reservoir |
| West Lake Sammamish, Washington | 17.5 mg/L | 1.4 ppt | 🟢 Soft | reservoir |
| Sammamish, Washington | 60 mg/L | 2.7 ppt | 🟡 Moderately Hard | reservoir |
| Maple Valley, Washington | 78 mg/L | 3.3 ppt | 🟡 Moderately Hard | reservoir |
National Benchmark
How Issaquah compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Issaquah | 44 mg/L | 🟢 None |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes Issaquah's Water Unique?
Local geology and source profile
Issaquah, Washington, in King County — a major east suburban Seattle community at the base of the Cascade Mountain foothills (Issaquah is surrounded by the Issaquah Alps — Tiger Mountain, Cougar Mountain, Squak Mountain — some of the most heavily used hiking terrain in the Pacific Northwest, directly accessible from the city), home of Costco's corporate headquarters (Costco Wholesale, one of the world's largest retailers by revenue, is headquartered in Issaquah — a major corporate presence in the east Seattle suburban economy), a rapidly growing tech and professional community adjacent to Microsoft's Redmond headquarters in the east King County tech corridor, and a diverse King County community — draws its municipal water supply from the Issaquah Creek watershed and Tolt River supply via the City of Issaquah. Water hardness in Issaquah measures 44 mg/L — classified as very soft.
Issaquah's very soft supply reflects the east King County Cascade foothills watershed's calcareous-poor geology. The Issaquah Creek and Tiger Mountain watershed drains: the Eocene Puget Group (calcareous-poor coal measures, sandstone, and shale of the Issaquah–Tiger Mountain area — the highly resistant calcareous-poor Eocene volcanic and sedimentary sequence); and the Quaternary calcareous-poor Cascade glacial outwash. The calcareous-poor east King County Cascade watershed produces the very soft 44 mg/L.
With hardness at 44 mg/L, Issaquah residents enjoy very soft water. City of Issaquah Water Division consistently delivers water meeting all Washington State DOE and EPA Safe Drinking Water Act requirements.
Geology & Source: River supply from the Issaquah Creek and Tiger Mountain watershed and Seattle Public Utilities (Tolt River) via the City of Issaquah Water Division or Eastside district supply — the King County east suburban Seattle Cascade foothills (Quaternary calcareous-poor Cascade volcanic glacial outwash and Eocene calcareous-poor Puget Group coal measures of the Issaquah Valley); very soft supply at 44 mg/L in King County.