State ranking
Highest regional evidence by state
Compare qualifying source-aligned regional observations by state, with medians, GPG, ranges, and evidence counts.
- 1South Dakota · 466 PPM
- 2North Dakota · 460 PPM
- 3Oklahoma · 398 PPM
National data rankings
Compare regional hardness evidence without pretending it is tap water.
These research tables use only the subset of regional observations that pass stricter source-alignment, distance, site-count, confidence, and recency rules. Every row links back to its evidence.
- State/DC profiles
- 51
- Qualifying cities
- 115
- Data through
- Sep 29, 2026
City ranking
Highest regional evidence by city
Compare city medians only when observations pass strict source, distance, site-count, confidence, and recency rules.
- 1Fargo, ND · 716 PPM
- 2Richfield, WI · 518 PPM
- 3Independence, MO · 487 PPM
State ranking
Lowest regional evidence by state
Start at the low end of the same national state dataset and see how much variation exists within each jurisdiction.
- 1Kentucky · 13 PPM
- 2Rhode Island · 20 PPM
- 3South Carolina · 26 PPM
City ranking
Lowest regional evidence by city
Explore the lowest qualifying city medians, with direct links to every city's evidence and local ZIP reports.
- 1Cranston, RI · 19 PPM
- 2East Providence, RI · 20 PPM
- 3Providence, RI · 20 PPM
What these rankings mean
A comparison tool, not a tap-water verdict
Comparisons use medians of qualifying regional environmental observations. A high position means more calcium-and-magnesium hardness in that evidence; it does not describe every utility or tap and does not mean the water is unsafe.
State results are not population weighted. City results require at least three eligible observations and two distinct monitoring sites. Low-confidence, distant, source-mismatched, coastal, and stale-only evidence is excluded.