Hardness
Moderately Hard
103.5 PPM · 6.1 GPG
Local water dashboard
Official source aggregationWater quality in Black Diamond, WA 98010
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.
1 reported benchmark flag
- Primary matched system
- Black Diamond Water Dept
- Source water
- Groundwater
- 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
0.0015 mg/L
10% of action level
Utility match
1 system
Serves 6,407 people system-wide
Hardness meter
How hard is the water?
Estimated local hardness
USGS hardness classification scale
103.5 PPM
Soft
0–59Moderate
60–120Hard
121–180Very hard
181+
0–59Moderate
60–120Hard
121–180Very hard
181+
Parts per million
103.5
mg/L as CaCO₃ equivalent
Grains per gallon
6.1
1 GPG ≈ 17.1 PPM
What this means at home
At 103.5 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
48
Nearest site
2.9 mi
Observation range
Jun 29, 2016–Aug 12, 2024
Estimate confidence
Moderate
Median of the latest qualifying hardness observation at each nearby monitoring site. Nearest monitoring location: 21N/06E-04B08 SWQA11 (Well).USGS source documentation ↗
Regional context
Is 98010 typical?
These comparisons use other indexed ZIP estimates, not utility tap samples. They help show local context without replacing a household test.
Black Diamond median
104 PPM
About the same1 indexed ZIP readings · Range 103.5–103.5 PPM
Washington median
104 PPM
About the same189 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.
1 pass1 fail
Lead (PB90)
0.0015 mg/L
Reported Dec 31, 2025
Copper (CU90)
1.7 mg/L
Reported Dec 31, 1996
Numerical coverage
2 comparable results
Missing values remain blank; absence is not treated as a pass.
Lead (90th percentile)
Measured in mg/L
Local 0.0015
EPA limit 0.015
Copper (90th percentile)
Measured in mg/L
Local 1.7
EPA limit 1.3
Share of EPA benchmark
100% line = listed limit
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 Black Diamond ZIP 98010 using 103.5 PPM nearby hardness and 2 reported measurement benchmarks.
Drinking water protection
Under-Sink Reverse Osmosis System
Copper (90th percentile) has a measured benchmark flag or active health-based SDWIS record in this profile.
A certified multi-stage RO system targets a broader range of dissolved contaminants at the kitchen tap.
Explore under-sink filtrationAffiliate 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 Black Diamond
Is tap water safe in Black Diamond?+
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 103.5 PPM, or 6.1 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.