01
Find the local profile
Search by ZIP or city to see the available hardness estimate, source distance, utility association, and compliance context.
Independent water-data guide
Understand the water coming into your home.
Find nearby hardness estimates, public water-system context, and practical explanations for more than 14,000 US ZIP profiles.
Search by city or ZIP. Results combine official USGS, EPA, and Census source data; they are not household tap tests.
14,060
Local ZIP profiles
51
States and DC
10,267
Indexed communities
13,840
Profiles with hardness data
Browse nationally
Start with your state
Every state and Washington, DC has a dedicated hub with its median, range, distribution, cities, utilities, and available ZIP profiles.
State hardness tile map
All 50 states plus DC. Color represents the median of available local estimates—not a single city marker.
Select or focus a tile for details
● Soft, 0–60● Moderate, 61–120● Hard, 121–180● Very hard, 181+
State median
South Dakota
516
PPM as CaCO₃
Very hard
234 hardness readings across 246 local profiles.
Explore SD →National snapshot
Most indexed profiles are not soft
The distribution below describes published profiles with an available nearby USGS hardness estimate. It is a summary of this index, not a population-weighted estimate of every US household.
206
National profile median PPM
0.2–2810
Observed profile range
Soft · 0–60 PPM
18%
2,552 profiles
Moderately hard · 61–120 PPM
15%
2,015 profiles
Hard · 121–180 PPM
11%
1,471 profiles
Very hard · 181+ PPM
56%
7,802 profiles
Compare places
Hardest indexed communities
Qualifying communities ranked by city median. Each has at least three readings, two with High or Moderate confidence, and two monitoring sites.
| Rank | Community | Hardness | GPG | Class | Report |
|---|---|---|---|---|---|
| #1 | Pascagoula, MS 3 indexed ZIP readings | 2395 PPM | 140.1 | Very Hard | View → |
| #2 | Biloxi, MS 4 indexed ZIP readings | 1885 PPM | 110.2 | Very Hard | View → |
| #3 | Gulfport, MS 3 indexed ZIP readings | 1805 PPM | 105.6 | Very Hard | View → |
| #4 | Fargo, ND 4 indexed ZIP readings | 711 PPM | 41.6 | Very Hard | View → |
| #5 | Rapid City, SD 3 indexed ZIP readings | 615 PPM | 36 | Very Hard | View → |
| #6 | Bismarck, ND 4 indexed ZIP readings | 503 PPM | 29.4 | Very Hard | View → |
| #7 | Independence, MO 7 indexed ZIP readings | 470 PPM | 27.5 | Very Hard | View → |
| #8 | San Luis, AZ 3 indexed ZIP readings | 449 PPM | 26.3 | Very Hard | View → |
| #9 | Odessa, TX 3 indexed ZIP readings | 421 PPM | 24.6 | Very Hard | View → |
| #10 | Richfield, WI 3 indexed ZIP readings | 417 PPM | 24.4 | Very Hard | View → |
Use the data well
From estimate to a sensible next step
A useful water decision separates mineral hardness, regulated contaminants, utility-wide reporting, and what is actually measured at your tap.
02
Check the evidence
Read the source dates and caveats. A nearby environmental sample and a utility-wide record answer different questions.
03
Test before treating
For health concerns or major equipment purchases, confirm conditions at the tap with a certified laboratory or current utility report.
Transparent by design
We show what the data can—and cannot—tell you.
Hard Water Index aggregates official public data. We retain source dates, matching methods, sample distance, missing values, and limitations instead of turning uncertainty into a confident claim.
Read the methodology- USGS
- Nearby hardness observations and site metadata
- EPA SDWIS
- Public water systems and compliance history
- US Census
- ZCTA and place geography used for local pages
- No invented zeros
- Unavailable measurements stay unavailable
Water guides
Learn before you buy or treat
Hardness basics
What Is Hard Water? A Practical Homeowner's Guide
Calcium and magnesium are behind scale, soap scum, and many treatment questions. Here is how to interpret the number without confusing hardness with safety.
7 min read
Reading results
PPM vs. GPG: How to Read Water Hardness Numbers
Water reports often use PPM while softener manuals use grains per gallon. The conversion is simple once the units and rounding are clear.
6 min read
Utility reports
How to Read Your Annual Water Quality Report
Your utility's annual report contains more than a pass-or-fail table. Learn which columns matter and what questions the report cannot answer about one tap.
8 min read