Cottage Lake Water Hardness & Quality Report (2026)
Water Hardness
2.9 grains per gallon
Source
reservoir
pH Level
7.4
neutral = 7.0
Lead
0.005 mg/L
✓ Below action level
TDS
107.5 mg/L
Est. Daily Cost
$0.13
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 Cottage Lake, your appliances are currently losing 7% efficiency due to mineral buildup.
| Appliance | In Cottage Lake | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 7.9 yrs | 8.5 yrs | -7% |
| Washing Machine | 11.8 yrs | 12 yrs | -2% |
| Water Heater | 13.6 yrs | 15 yrs | -9% |
Regional Water Comparison
How Cottage Lake compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ Cottage Lake, Washington | 50 mg/L | 2.4 ppt | 🟢 Soft | reservoir |
| Union Hill-Novelty Hill, Washington | 68.5 mg/L | 3 ppt | 🟡 Moderately Hard | reservoir |
| Redmond, Washington | 24.5 mg/L | 1.6 ppt | 🟢 Soft | reservoir |
| Sammamish, Washington | 60 mg/L | 2.7 ppt | 🟡 Moderately Hard | reservoir |
| Kingsgate, Washington | 79.5 mg/L | 3.4 ppt | 🟡 Moderately Hard | reservoir |
National Benchmark
How Cottage Lake compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Cottage Lake | 50 mg/L | 🟢 None |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes Cottage Lake's Water Unique?
Local geology and source profile
Cottage Lake, Washington, in King County on the Sammamish Plateau near Woodinville and Redmond — a desirable King County lakefront community surrounded by Marymoor Park, the Tolt Pipeline Trail, and Novelty Hill wine country — receives its municipal water from the Cascade Water Alliance or King County Water District 45, which draws from the Tolt River Watershed Reservoir in the Cascade Mountains east of the plateau. The Tolt River supply is one of the Seattle-area regional water system's two primary Cascade Mountain sources.
The very soft 50 mg/L hardness and low TDS of 107.5 mg/L reflect the Tolt River watershed's pristine Cascade Mountain geology. The Tolt River drains the Western Cascades volcanic terrain — Oligocene and Miocene andesitic and basaltic volcanic rocks (Ohanapecosh and Stevens Ridge formations), Eocene marine sedimentary rocks, and the Snoqualmie Batholith granodiorite pluton in the high Cascades headwaters. These igneous and metamorphic rock terrains, lacking carbonate minerals, yield characteristically soft, mineral-poor water. The Tolt Reservoir provides protective storage, and the Cascade Water Alliance's modern treatment ensures consistent water quality for the Sammamish Plateau communities.
At 50 mg/L, Cottage Lake's water is very soft — excellent for household appliances and comfortable for all uses. Scale forms slowly over many months in kettles and appliances, soap lathers generously, and the dishwasher produces spotless results. Semi-annual descaling of heating appliances is adequate. The PFAS level of 2.4 ppt is excellent — among the cleanest in the greater Seattle metro dataset — reflecting the Tolt River's well-protected Cascade Mountain watershed, limited industrial land use in the upper Tolt catchment, and the predominantly residential nature of the Cottage Lake-Woodinville corridor.
Geology & Source: Cottage Lake in King County is served by the Cascade Water Alliance or King County Water District drawing from the Tolt River or Cedar River watershed reservoirs — the Cascade Range Tolt and Cedar watersheds drain Oligocene and Miocene volcanic rocks (Keechelus andesitic volcanics, Snoqualmie plutonic complex) with negligible carbonate — Cascade volcanic watershed drainage produces very soft water at 50 mg/L with low TDS 108 mg/L on the eastern Sammamish Plateau.