How hard is the water in Sammamish, WA?

Tap water hardness
62mg/L
3.6gpg
Moderately hard

Reported by Sammamish Plateau Water & Sewer · August 2025

WA typical
36 mg/L
EPA health violations since 2016
0
Softener for 3 people
24k grain
Data
Utility report

Tap water in Sammamish has about 62 mg/L of hardness, which is 3.6 grains per gallon. On the USGS scale that counts as moderately hard. The number comes from Sammamish Plateau Water & Sewer, dated August 2025.

Sammamish on the hardness scale, with nearby cities
060120180240300360+WA typical 36Duvall: 21 mg/LDuvall 21Newcastle: 27 mg/LNewcastle 27East Renton Highlands: 30 mg/LEast Renton Highlands 30Bellevue: 34 mg/LBellevue 34Kirkland: 34 mg/LKirkland 34Redmond: 39 mg/LRedmond 39Mercer Island: 39 mg/LMercer Island 39Issaquah: 41 mg/LIssaquah 41Snoqualmie: 41 mg/LSnoqualmie 41Union Hill-Novelty Hill: 50 mg/LUnion Hill-Novelty Hill 50Sammamish 62mg/L as calcium carbonate060120180240300360+WA 36Newcastle: 27 mg/LNewcastle 27East Renton Highlands: 30 mg/LEast Rento. 30Bellevue: 34 mg/LBellevue 34Redmond: 39 mg/LRedmond 39Issaquah: 41 mg/LIssaquah 41Union Hill-Novelty Hill: 50 mg/LUnion Hill. 5062 mg/Lmg/L as calcium carbonate
Soft 0–60 mg/LModerately hard 61–120 mg/LHard 121–180 mg/LVery hard 181+ mg/L

At 62 mg/L, Sammamish is 26 mg/L above the typical Washington figure of 36. None of the 10 nearest cities we track has harder water. The range nearby runs from 21 mg/L in Duvall to 50 in Union Hill-Novelty Hill.

What 62 mg/L means at home

You may see faint white spots on glasses and shower doors after the water dries.

Scale builds up slowly. A kettle or coffee maker needs descaling now and then, maybe every few months.

Hardness is not a health problem, and EPA sets no limit for it. It is a matter of scale and soap.

What to do about it

Optional. Plenty of households at this level live with it and descale the kettle now and then.

Water softener

Worth a look if spots on glass bother you, or if your tankless water heater manual asks for softer water.

Carbon filter

Improves taste and removes chlorine. It leaves calcium and magnesium in place.

Softener size for Sammamish

3 people × 75 gallons a day × 3.6 gpg = 821 grains a day. A 24,000-grain unit regenerates about every 29 days.

Size it for your household

EPA record for Sammamish's water system

Sammamish Plateau Water & Sewer · PWSID WA5340900

No health-based violations since 2016

Serves about 79,362 people from surface water.

Health-based
0
Monitoring or reporting
0
Open now
0

Health-based means a contaminant above its legal limit or a missed treatment step. Monitoring and reporting violations are late or missing tests and notices. Source: EPA ECHO, 2026Q3 export, violations with periods starting 2016 or later. Full EPA record.

Questions

Is Sammamish water hard?

Somewhat. It measures about 62 mg/L (3.6 grains per gallon), which the USGS classes as moderately hard.

What is the water hardness in Sammamish in grains per gallon?

About 3.6 gpg. One grain per gallon equals 17.1 mg/L, so 62 mg/L divided by 17.1 gives 3.6.

What size water softener do I need in Sammamish?

For 3 people using 75 gallons each per day, 3.6 gpg works out to about 821 grains a day. A 24,000-grain softener covers that with a regeneration about every 29 days.

Has the Sammamish water system had EPA violations?

EPA records show no health-based violations for Sammamish Plateau Water & Sewer since 2016.

Nearby cities

All 145 cities in Washington

Hardness data: TapWaterData US Water Hardness (utility report, August 24, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.