Hardness
Moderately Hard
61.3 PPM · 3.6 GPG
Local water dashboard
Official source aggregationWater quality in Mercer Island, WA 98040
A source-transparent look at local hardness, associated public water systems, EPA compliance history, and the measurements that are—and are not—available for King County.
No active health-based violation reported
- Primary matched system
- Mercer Island City Of
- Source water
- Surface water
- County
- King County
- Profile updated
At a glance
What the current records say
EPA quarter 2026Q2
Compliance screen
No active flag
0 active health-based records
Lead 90th percentile
Not reported
Check the utility CCR or tap test
Utility match
1 system
Serves 31,057 people system-wide
Hardness meter
How hard is the water?
Estimated local hardness
USGS hardness classification scale
61.3 PPM
Soft
0–59Moderate
60–120Hard
121–180Very hard
181+
0–59Moderate
60–120Hard
121–180Very hard
181+
Parts per million
61.3
mg/L as CaCO₃ equivalent
Grains per gallon
3.6
1 GPG ≈ 17.1 PPM
What this means at home
At 61.3 PPM, mineral scale can build up on fixtures and heating elements, reduce soap lather, and leave visible spotting. Hardness is primarily an aesthetic and appliance concern—not itself a tap-water safety rating.
USGS sites used
2
Nearest site
25.4 mi
Observation range
Jan 13, 2016–Mar 20, 2026
Estimate confidence
Low
Median of the latest qualifying hardness observation at each nearby monitoring site. Nearest monitoring location: Clarks Creek at Hatchery near Puyallup, WA (Stream).USGS source documentation ↗
Regional context
Is 98040 typical?
These comparisons use other indexed ZIP estimates, not utility tap samples. They help show local context without replacing a household test.
Mercer Island median
61 PPM
About the same1 indexed ZIP readings · Range 61.3–61.3 PPM
Washington median
104 PPM
43 PPM lower189 indexed ZIP readings · Range 20.6–238 PPM
EPA benchmark screen
Contaminant snapshot
Available numerical results from associated SDWIS community water systems, compared with the applicable action level or federal MCL. Federal measured-value coverage is incomplete.
Lead (PB90)
Not available
No numerical 90th-percentile result
Copper (CU90)
Not available
No numerical 90th-percentile result
Numerical coverage
0 comparable results
Missing values remain blank; absence is not treated as a pass.
No comparable measured values reported
Federal SDWIS data does not contain a numerical result and matching benchmark for this profile. Review the compliance history and the utility's Consumer Confidence Report instead.
2026Q2
- All records
- 0
- Health-based
- 0
- Active health-based
- 0
No violation record was returned for the associated systems in the imported lookback window beginning Jan 1, 2021.
No reported violation does not prove that every contaminant was tested or absent; SDWIS measured values are incomplete and lag state records.
Solutions matcher
Your personalized water action plan
Matched to Mercer Island ZIP 98040 using 61.3 PPM nearby hardness and 0 reported measurement benchmarks.
No urgent match
Start with an independent water test
This profile does not trigger a treatment recommendation. Test at the tap before investing in equipment.
Affiliate disclosure: we may earn a commission from qualifying purchases, at no added cost to you. Product matching is educational and does not replace certified water testing.
Frequently asked
Water questions for Mercer Island
Is tap water safe in Mercer Island?+
EPA ECHO shows no active health-based violation for the associated systems in this reporting snapshot. This does not prove every contaminant is absent; federal records can lag and household plumbing can change tap conditions.
How hard is the water?+
Nearby USGS observations produce an estimate of 61.3 PPM, or 3.6 grains per gallon, classified as moderately hard. This is not a household tap measurement.
Do I need a water softener?+
There is no high-hardness trigger in this profile. Confirm with a tap test before buying equipment.