Mountlake Terrace Water Hardness & Quality Report (2026)
Water Hardness
3.4 grains per gallon
Source
reservoir
pH Level
7.5
neutral = 7.0
Lead
0.006 mg/L
✓ Below action level
TDS
134.5 mg/L
Est. Daily Cost
$0.16
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 Mountlake Terrace, your appliances are currently losing 8% efficiency due to mineral buildup.
| Appliance | In Mountlake Terrace | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 7.7 yrs | 8.5 yrs | -9% |
| Washing Machine | 11.4 yrs | 12 yrs | -5% |
| Water Heater | 13.3 yrs | 15 yrs | -11% |
Regional Water Comparison
How Mountlake Terrace compares to its nearest neighbours
| City | Hardness | PFAS (ppt) | Risk | Source |
|---|---|---|---|---|
| ▶ Mountlake Terrace, Washington | 58.5 mg/L | 2.7 ppt | 🟢 Soft | reservoir |
| Lynnwood, Washington | 70 mg/L | 3.1 ppt | 🟡 Moderately Hard | reservoir |
| Lake Forest Park, Washington | 21.5 mg/L | 1.5 ppt | 🟢 Soft | reservoir |
| Shoreline, Washington | 15 mg/L | 1.3 ppt | 🟢 Soft | reservoir |
| Bothell West, Washington | 36.5 mg/L | 2 ppt | 🟢 Soft | reservoir |
National Benchmark
How Mountlake Terrace compares to the USA average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Mountlake Terrace | 58.5 mg/L | 🟢 None |
| USA National Avg | 150 mg/L | 🟠 Moderate |
| Badger Top Rated | 8.5 mg/L | 🟢 None |
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What Makes Mountlake Terrace's Water Unique?
Local geology and source profile
Mountlake Terrace, Washington, in Snohomish County — a southern Snohomish County suburb directly north of Seattle and Shoreline, a dense first-ring suburb in the Seattle-Everett corridor, home of Mountlake Terrace High School and a transit-oriented community on the Swift BRT corridor — receives its municipal water from the Mountlake Terrace Water Division or the Alderwood Water and Wastewater District, which draws from Spada Lake (Culmback Dam) on the Sultan River in the North Cascades, through the Everett regional water supply, or from Seattle Public Utilities (SPU) through the south Snohomish County regional connection.
The moderately soft 58.5 mg/L hardness and TDS of 134.5 mg/L reflect the North Cascade supply's crystalline geological character — consistent with the Everett-Spada Lake and Seattle-Tolt/Cedar supplies throughout the greater Seattle regional water network. The Sultan River-Spada Lake and Tolt River watersheds drain high-grade Precambrian-Paleozoic metamorphic rocks (Skagit Gneiss) and Jurassic-Cretaceous metavolcanic belts — carbonate-free crystalline terrain producing characteristically soft Pacific Northwest mountain water. The moderately soft reading (58.5 mg/L) is typical for Snohomish County communities on the Everett-Spada Lake supply.
At 58.5 mg/L, Mountlake Terrace's water is moderately soft — comfortable for household use. Scale forms slowly over many months, soap lathers well, and appliances operate efficiently. Semi-annual descaling is adequate. The PFAS level of 2.7 ppt is very good — Mountlake Terrace's residential character, the pristine North Cascade watershed supply, and the relatively limited direct military-industrial PFAS sources in the South Snohomish County corridor produce a modest background.
Geology & Source: Mountlake Terrace in Snohomish County draws from the Mountlake Terrace Water or Alderwood Water and Wastewater District on Spada Lake (Sultan River) via Seattle Public Utilities or Everett Water — the Sultan River drains the North Cascade Range (Skagit Gneiss and Jurassic metavolcanic crystalline terrain) — North Cascade crystalline watershed drainage produces moderately soft water at 58.5 mg/L with TDS 135 mg/L in this Snohomish County suburb.