State distribution
Hardness across indexed ZIPs
Counts describe published ZIP profiles, not a population-weighted statewide sample.
Soft · 0–60 PPM0
Moderately hard · 61–120 PPM57
Hard · 121–180 PPM0
Very hard · 181+ PPM0
State water index
District of Columbia water hardness
Search 1 indexed communities and 57 ZIP profiles, then compare the underlying utility, source, distance, and reporting context.
Median regional evidence
73PPM
Moderately Hard
Indexed range 70.6–73.3 PPM
- ZIP profiles
- 57
- Cities
- 1
- Matched utilities
- 1
- Counties
- 1
Understanding District of Columbia
Why local comparisons matter here
Washington, DC is served primarily through a regional Potomac River treatment system, so many ZIP profiles share utility-wide records even though building plumbing differs by address.
In this index, moderately hard is the largest category, covering 57 of 57 profiles with hardness data. The state median is 73 PPM, but the full indexed range is 70.6–73.3 PPM.
Evidence coverage
What the current records support
- Hardness estimate
- 100%
- Lead 90th percentile
- 100%
- Copper 90th percentile
- 0%
0
Low-confidence hardness profiles
57
Research-comparison eligible profiles
Reported source water
Utility source mix
- Surface water
- 1
Highest medians
Highest eligible city medians
- 1. Washington73 PPM
Lowest medians
Lowest eligible city medians
- 1. Washington73 PPM
City directory
Explore District of Columbia by city
Search by city or county, then sort by name, hardness, or ZIP coverage.
1 cities · 57 ZIP profiles
County comparison
Highest regional-evidence county medians
| County | Median | Range | ZIP profiles |
|---|---|---|---|
| District Of Columbia County | 73 PPM | 70.6–73.3 | 57 |