Does a high water-hardness rank mean the water is unsafe?

No. Hardness mainly describes dissolved calcium and magnesium and scale potential. It is not a drinking-water safety score or contaminant ranking.

US regional hardness research

Highest regional hardness evidence by state

This research table starts with the highest state median among observations that meet the strict ranking rule. It compares regional environmental evidence, not utility-treated or household tap water.

Complete table

51 state and DC profiles

Data through Sep 29, 2026

Highest regional hardness evidence by state
Rank	State	Median	Class	Observed range	Evidence	Eligible
1	South Dakota	466 PPM27.3 GPG	Very Hard	309.5–830 PPM	9 readings	100%strict rule
2	North Dakota	460 PPM26.9 GPG	Very Hard	96.4–718.5 PPM	32 readings	100%strict rule
3	Oklahoma	398 PPM23.3 GPG	Very Hard	45.5–398 PPM	5 readings	100%strict rule
4	Indiana	348 PPM20.4 GPG	Very Hard	121–420 PPM	83 readings	100%strict rule
5	Utah	348 PPM20.4 GPG	Very Hard	195–552 PPM	43 readings	100%strict rule
6	Michigan	343 PPM20.1 GPG	Very Hard	108–417.5 PPM	39 readings	100%strict rule
7	Ohio	336 PPM19.6 GPG	Very Hard	87–374 PPM	6 readings	100%strict rule
8	Illinois	325 PPM19 GPG	Very Hard	131–423 PPM	91 readings	100%strict rule
9	Nebraska	304 PPM17.8 GPG	Very Hard	215–703 PPM	202 readings	100%strict rule
10	Wisconsin	291 PPM17 GPG	Very Hard	135–540 PPM	101 readings	100%strict rule
11	Florida	282 PPM16.5 GPG	Very Hard	135–816.5 PPM	179 readings	100%strict rule
12	Iowa	274 PPM16 GPG	Very Hard	237–472 PPM	64 readings	100%strict rule
13	Wyoming	229 PPM13.4 GPG	Very Hard	174–229 PPM	3 readings	100%strict rule
14	Kansas	221 PPM12.9 GPG	Very Hard	80.9–292 PPM	55 readings	100%strict rule
15	California	215 PPM12.6 GPG	Very Hard	65.8–539.5 PPM	241 readings	100%strict rule
16	Missouri	205 PPM12 GPG	Very Hard	23.8–486.5 PPM	82 readings	100%strict rule
17	Washington	205 PPM12 GPG	Very Hard	109.5–308.5 PPM	22 readings	100%strict rule
18	New Mexico	197 PPM11.5 GPG	Very Hard	18.3–677.5 PPM	66 readings	100%strict rule
19	Colorado	191 PPM11.2 GPG	Very Hard	7.2–882.5 PPM	58 readings	100%strict rule
20	Minnesota	191 PPM11.2 GPG	Very Hard	180.5–716 PPM	37 readings	100%strict rule
21	West Virginia	145 PPM8.5 GPG	Hard	74.1–344.5 PPM	41 readings	100%strict rule
22	New York	135 PPM7.9 GPG	Hard	5.5–385.5 PPM	405 readings	100%strict rule
23	Louisiana	133 PPM7.8 GPG	Hard	28.4–411 PPM	21 readings	100%strict rule
24	Texas	118 PPM6.9 GPG	Moderately Hard	23.6–310 PPM	315 readings	100%strict rule
25	Pennsylvania	111 PPM6.5 GPG	Moderately Hard	23.6–219 PPM	117 readings	100%strict rule
26	Idaho	110 PPM6.4 GPG	Moderately Hard	95.3–161 PPM	8 readings	100%strict rule
27	Vermont	91 PPM5.3 GPG	Moderately Hard	19.3–163.5 PPM	2 readings	100%strict rule
28	Connecticut	89 PPM5.2 GPG	Moderately Hard	15.8–137.5 PPM	84 readings	100%strict rule
29	Maryland	83 PPM4.9 GPG	Moderately Hard	27.7–145 PPM	17 readings	100%strict rule
30	New Jersey	79 PPM4.6 GPG	Moderately Hard	12.6–296.5 PPM	83 readings	100%strict rule
31	Arkansas	79 PPM4.6 GPG	Moderately Hard	7.8–489 PPM	67 readings	100%strict rule
32	Massachusetts	76 PPM4.4 GPG	Moderately Hard	10.1–208.5 PPM	177 readings	100%strict rule
33	Alabama	76 PPM4.4 GPG	Moderately Hard	5.5–217.5 PPM	17 readings	100%strict rule
34	New Hampshire	74 PPM4.3 GPG	Moderately Hard	58–104.5 PPM	9 readings	100%strict rule
35	District of Columbia	73 PPM4.3 GPG	Moderately Hard	70.6–73.3 PPM	57 readings	100%strict rule
36	Georgia	69 PPM4 GPG	Moderately Hard	8.8–214 PPM	153 readings	100%strict rule
37	Montana	69 PPM4 GPG	Moderately Hard	32.4–105.5 PPM	2 readings	100%strict rule
38	Nevada	66 PPM3.9 GPG	Moderately Hard	61–177 PPM	18 readings	100%strict rule
39	Delaware	63 PPM3.7 GPG	Moderately Hard	31.1–129 PPM	47 readings	100%strict rule
40	Hawaii	57 PPM3.3 GPG	Soft	56.3–57.1 PPM	6 readings	100%strict rule
41	Arizona	55 PPM3.2 GPG	Soft	54–481 PPM	85 readings	100%strict rule
42	Mississippi	55 PPM3.2 GPG	Soft	14.5–286 PPM	19 readings	100%strict rule
43	Alaska	52 PPM3 GPG	Soft	48.9–54.5 PPM	2 readings	100%strict rule
44	Tennessee	51 PPM3 GPG	Soft	13.4–276 PPM	120 readings	100%strict rule
45	North Carolina	50 PPM2.9 GPG	Soft	4.8–256 PPM	109 readings	100%strict rule
46	Maine	36 PPM2.1 GPG	Soft	35.5–35.6 PPM	6 readings	100%strict rule
47	Oregon	35 PPM2 GPG	Soft	18.4–42.6 PPM	34 readings	100%strict rule
48	Virginia	35 PPM2 GPG	Soft	9–306 PPM	31 readings	100%strict rule
49	South Carolina	26 PPM1.5 GPG	Soft	3–107 PPM	12 readings	100%strict rule
50	Rhode Island	20 PPM1.2 GPG	Soft	14.6–65.5 PPM	29 readings	100%strict rule
51	Kentucky	13 PPM0.8 GPG	Soft	12.6–12.6 PPM	1 readings	100%strict rule

Ranking methodology

How this state ranking is calculated

We group only ranking-eligible regional observations by state and compare their medians. Eligibility requires source-type alignment, multiple sites, recent evidence, non-low confidence, and a nearest site within 10 miles. Results are not population weighted.

The indexed range shows why the median needs context: communities within one state may use different aquifers, rivers, reservoirs, or blends. The Supported column is the share of observations that pass the stricter distance, source alignment, site-count, and recency rules in our methodology.

Quick answer

Which state has the hardest qualifying regional hardness evidence?

South Dakota is first in this research comparison with a qualifying regional median of 466 PPM (27.3 GPG), based on 9 observations.

This result describes qualifying regional environmental evidence. It must not be generalized to a utility or address without a current utility report or tap measurement.

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