Mountlake Terrace Water Hardness & Quality Report (2026)

Water Hardness

58.5mg/L

Soft

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: See methodology section below · Updated 2026

58.5mg/L as CaCO₃Soft

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	7.8 yrs	8.5 yrs	-8%
Washing Machine	11 yrs	12 yrs	-8%
Water Heater	13.8 yrs	15 yrs	-8%

Regional Water Comparison

How Mountlake Terrace compares to its nearest neighbours

City	Hardness	Risk	Source
▶ Mountlake Terrace, Washington	58.5 mg/L	🟢 Soft	reservoir
Lynnwood, Washington	12.4 mg/L	🟢 Soft	reservoir
Lake Forest Park, Washington	≈ 120–179 mg/L	🟠 Hard	groundwater
Shoreline, Washington	≈ 0–60 mg/L	🟢 Soft	reservoir
Bothell West, Washington	≈ 120–179 mg/L	🟠 Hard	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	151 mg/L	🟠 Moderate
Scarsdale Top Rated	0.02 mg/L	🟢 None

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What Makes Mountlake Terrace's Water Unique?

Local geology and source profile

Source: ReservoirTDS: 134.5 mg/LpH: 7.5

Mountlake Terrace is served by the City of Mountlake Terrace Water Utility, located at 23204 58th Avenue West, Mountlake Terrace, WA 98043. The utility operates as a surface water system, purchasing treated water from external sources rather than operating its own treatment plants. The service area encompasses the city and surrounding communities in the Seattle metropolitan region; residents can contact the utility at 425-670-8264 or cityhall@mltwa.gov with questions.

The water supply originates from surface water sources likely drawn from regional reservoirs or rivers serving the greater Puget Sound area. The watershed geology reflects the Puget Sound lowlands, characterized by Quaternary glacial deposits, alluvial plains, and sedimentary formations typical of the Pacific Northwest. This geological setting, shaped by glacial history and regional precipitation patterns, produces water with moderate mineral content.

Mountlake Terrace's tap water meets all EPA safety standards, with only 3 total violations recorded since 2023, and drinking water falling significantly below EPA action levels. The water system has reported 1 contaminant above EPA health-based guidelines (MCLGs) in at least one area served. Residents with scale concerns or water quality questions should contact the utility directly; annual Drinking Water Quality Reports (Consumer Confidence Reports) detail all tested parameters, treatment processes, and compliance status.

Geology & Source: Cascade Range watershed — water passes through Quaternary glacial deposits and alluvial formations of the Puget Sound lowlands; sedimentary geology contributes moderate mineral content

Other Washington Water Reports

Lynnwood

12.4 mg/L

🟢 Soft

Lake Forest Park

≈ 120–179 mg/L

🟠 Hard

Shoreline

≈ 0–60 mg/L

🟢 Soft

Bothell West

≈ 120–179 mg/L

🟠 Hard

Report an Issue

Notice an error or missing data? Help us keep this page accurate. If you spot incorrect water hardness, outdated utility info, or missing details, please let us know.

All reports are reviewed by our team. Thank you for supporting data quality!

Frequently Asked Questions

Is Mountlake Terrace's water safe to drink?

Yes. Mountlake Terrace's water meets all federal safety standards. The hardness is 58.5 mg/L (Soft), which is safe to drink. High hardness affects appliances and taste, but poses no health risk.

Do I need a water softener in Mountlake Terrace?

Mountlake Terrace's water is soft at 58.5 mg/L. A water softener is generally not necessary, though a carbon filter can improve taste and remove any remaining chlorine.

How does Mountlake Terrace compare to the USA average?

The USA national average is 151 mg/L. Mountlake Terrace (58.5 mg/L) is 92 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 Mountlake Terrace 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.