How does Sammamish's water compare to the national average?

The USA national average is 151 mg/L. Sammamish (≈ 60–119 mg/L) is 61 mg/L softer than average.

Sammamish Water Hardness & Quality Report (2026)

Water Hardness

moderately hard

~60–119 mg/L

Moderately Hard

estimated · not lab-verified

Source

reservoir

pH Level

7.6

neutral = 7.0

Lead

0.006 mg/L

✓ Below action level

TDS

139.4 mg/L

Est. Daily Cost

$0.24

energy & soap waste

Source: See methodology section below · Updated 2026

moderately hard~60–119 mg/LModerately Hard · est.

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 Sammamish, your appliances are currently losing 12% efficiency due to mineral buildup.

Appliance	In Sammamish	Soft Water City	Efficiency Loss
Kettle	7.5 yrs	8.5 yrs	-12%
Washing Machine	10.6 yrs	12 yrs	-12%
Water Heater	13.2 yrs	15 yrs	-12%

Regional Water Comparison

How Sammamish compares to its nearest neighbours

City	Hardness	PFAS (ppt)	Risk	Source
▶ Sammamish, Washington	≈ 60–119 mg/L	143.9 ppt	🟡 Moderately Hard	reservoir
Redmond, Washington	90 mg/L	13.4 ppt	🟡 Moderately Hard	reservoir
City of Sammamish, Washington	≈ 120–179 mg/L	143.9 ppt	🟠 Hard	reservoir
Union Hill-Novelty Hill, Washington	≈ 120–179 mg/L	3 ppt	🟠 Hard	groundwater
West Lake Sammamish, Washington	≈ 0–60 mg/L	1.4 ppt	🟢 Soft	reservoir

National Benchmark

How Sammamish compares to the USA average

Benchmark	Hardness	Appliance Risk
▶ Sammamish	≈ 60–119 mg/L	🟡 Low
USA National Avg	151 mg/L	🟠 Moderate
Scarsdale Top Rated	0.02 mg/L	🟢 None

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What Makes Sammamish's Water Unique?

Local geology and source profile

Source: ReservoirTDS: 139.4 mg/LpH: 7.6

Sammamish Plateau Water & Sewer District (SPW&SD) is the primary utility serving Sammamish and surrounding areas in King County, Washington. The district maintains a mixed supply portfolio, drawing from both groundwater via local production wells and surface water purchased from the City of Everett. Annual Drinking Water Reports (Consumer Confidence Reports) are published as required by the EPA and the Washington Department of Health under the Safe Drinking Water Act, documenting sources, treatment processes, and water quality across the service area in the Puget Sound lowlands.

The Sammamish Plateau is situated in the Puget Sound lowlands, characterized by Quaternary glacial deposits overlying Tertiary marine sedimentary rocks. The district's groundwater production wells tap into these mineral-bearing glacial and sedimentary strata, contributing moderate hardness to local supply. Surface water purchased from the City of Everett is comparatively soft. This mixed-source approach reflects the region's complex hydrogeology, where glacial-era geology influences water chemistry and mineral content differently across the service territory.

Because SPW&SD blends groundwater and surface sources, scale buildup potential varies by location — groundwater-fed areas may experience moderate mineral deposits in water heaters, dishwashers, and fixtures over time. Regular vinegar descaling and periodic aerator cleaning help manage these effects. Customers should consult their specific Annual Drinking Water Report or contact the district directly to determine hardness at their address; a water softener may be worthwhile for properties primarily served by local production wells.

Geology & Source: Sammamish Plateau, King County; Quaternary glacial deposits overlying Tertiary marine sedimentary rocks — groundwater wells contact mineral-bearing strata contributing moderate hardness; surface supply from City of Everett remains soft

Other Washington Water Reports

Redmond

90 mg/L

🟡 Moderately Hard

City of Sammamish

≈ 120–179 mg/L

🟠 Hard

Union Hill-Novelty Hill

≈ 120–179 mg/L

🟠 Hard

West Lake Sammamish

≈ 0–60 mg/L

🟢 Soft

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Frequently Asked Questions

Is Sammamish's water safe to drink?

Yes. Sammamish's water meets all federal safety standards. The hardness is ≈ 60–119 mg/L (Moderately Hard), which is safe to drink. High hardness affects appliances and taste, but poses no health risk.

Do I need a water softener in Sammamish?

Sammamish's water is moderately hard at ≈ 60–119 mg/L. A water softener is generally not necessary, though a carbon filter can improve taste and remove any remaining chlorine.

How does Sammamish compare to the USA average?

The USA national average is 151 mg/L. Sammamish (≈ 60–119 mg/L) is 61 mg/L below the national average. The softest major city is Scarsdale at just 0.02 mg/L.

Data Sources & Methodology

Water quality data for Sammamish is derived from geographic and geological modelling of the surrounding region. No federal monitoring station data was available for this location.

Estimated

Water Hardness

Modelled estimate based on state-level USGS geological survey data for this region. No direct USGS Water Quality Portal measurement was matched to this city — the value reflects a statistical range calibrated to the state's dominant rock types and typical source water characteristics.

Estimated

Estimated from regional geology and source water characteristics. pH is correlated with water hardness and local bedrock — values may differ from utility-reported figures.

Estimated

TDS — Total Dissolved Solids

Estimated using a derived ratio from water hardness and regional conductance profiles. TDS in natural water correlates strongly with total mineral content including hardness ions.

Measured

PFAS — Perfluoroalkyl and Polyfluoroalkyl Substances

EPA UCMR5 (5th Unregulated Contaminant Monitoring Rule, 2023–2025) — sum of PFAS compounds detected at the public water system serving this city. A value of 0 indicates the system was sampled with no detection above reporting limits.

Modelled

Lead

Modelled estimate based on the EPA Lead and Copper Rule 90th-percentile tap-sample methodology. No publicly available per-city lead dataset with sufficient national coverage exists. Values are a conservative baseline derived from city population tier and infrastructure age — all estimates are maintained below the EPA action level of 0.015 mg/L.

Calculated

Appliance Lifespan

Calculated from water hardness using a linear degradation model. Baseline lifespans represent soft-water performance (kettle: 8.5 yrs, washing machine: 12.0 yrs, water heater: 15.0 yrs). Hard water mineral scale progressively reduces operational life in direct proportion to hardness concentration.