Which state has the hardest water?

Nevada has the highest estimate in this historical comparison with an average of 17.5 GPG (300 PPM), driven by Lake Mead and desert basin groundwater. Indiana (17.4 GPG), Arizona (16.4 GPG), and Texas (15.7 GPG) are close behind.

Which state has the softest water?

Arkansas has the lowest estimate in this historical comparison with an average of just 2.2 GPG (38 PPM). Massachusetts (2.9 GPG), Hawaii (3.5 GPG), Maine (3.5 GPG), and New Hampshire (3.5 GPG) also have naturally soft water.

Why is water hardness so different between states?

Water hardness depends on geology. States with limestone, dolomite, and other carbonate rock formations (like those in the Southwest and Midwest) have hard water because these rocks dissolve calcium and magnesium into the water supply. States with granite and volcanic rock (Pacific Northwest, Northeast) have naturally soft water.

Can water hardness vary within a state?

Yes, significantly. State averages can mask large internal variations. For example, in New York, NYC has very soft water (1.8 GPG) while Western NY is quite hard. In California, San Francisco is soft (1.5 GPG) while Southern California can exceed 15 GPG. Always check city-level data when possible.

How was this map data collected?

The map uses historical research estimates, not a verified official dataset of state tap-water averages. They have not been verified as population-weighted averages and should not be used for equipment settings. For the most accurate reading of your home water, we recommend using a home test kit.

Water Hardness Map of the United States

Hover over any state to see its indicative historical estimate. Indicative historical estimates; use the municipal sources for verified local figures.

Soft (0–1 GPG)

Slightly Hard (1–3.5 GPG)

Moderately Hard (3.5–7 GPG)

Hard (7–10.5 GPG)

Very Hard (10.5–25+ GPG)

Key Findings

Hardest Water Regions

The Southwest (NV, AZ, TX, NM, UT) and Great Plains (KS, NE, IN) have the hardest water, driven by limestone aquifers and Colorado River mineral content.

Softest Water Regions

New England (MA, ME, NH) and the Pacific Northwest (OR, WA) have the softest water, thanks to granite bedrock and protected mountain watersheds.

National Average

The US average is approximately 7 GPG (120 PPM), right at the threshold where water treatment starts to become beneficial.

State Variation

Water hardness can vary dramatically within a state. City-level data is always more accurate than state averages for treatment decisions.

All States Ranked by Water Hardness

#	State	GPG	PPM	Level	Sources
1	Nevada	17.5	300	Very Hard	Surface (L. Mead) and Groundwater
2	Indiana	17.4	298	Very Hard	Groundwater and Surface Blends
3	Arizona	16.4	280	Very Hard	Surface (Colorado R.) and Groundwater
4	Texas	15.7	268	Very Hard	Surface and Groundwater
5	Utah	15.1	259	Very Hard	Surface and Groundwater
6	New Mexico	14.7	252	Very Hard	Groundwater and Surface
7	Kansas	14.6	250	Very Hard	Groundwater (Ogallala/High Plains)
8	Nebraska	12.3	210	Very Hard	Groundwater (Ogallala)
9	Oklahoma	12.3	210	Very Hard	Surface and Groundwater
10	Wyoming	12.3	210	Very Hard	Surface and Groundwater
11	California	11.7	200	Very Hard	Surface (SWP) and Groundwater
12	Delaware	11.7	200	Very Hard	Groundwater (94% reliance)
13	Florida	11.7	200	Very Hard	Groundwater (Floridan Aquifer)
14	Missouri	11.7	200	Very Hard	Surface (Missouri R.) and Ground
15	Colorado	10.8	185	Very Hard	Surface (Snowmelt) and Groundwater
16	Minnesota	10.2	175	Hard	Surface (Mississippi) and Groundwater
17	Alabama	8.8	150	Hard	Surface and Groundwater
18	South Dakota	8.8	150	Hard	Surface and Groundwater
19	Michigan	8.2	140	Hard	Surface (Lakes) and Groundwater
20	Wisconsin	8.2	140	Hard	Surface and Groundwater
21	District of Columbia	7.9	135	Hard	Surface (Potomac River)
22	Georgia	7.6	130	Hard	Surface and Groundwater
23	Iowa	7.6	130	Hard	Groundwater (75% reliance)
24	North Dakota	7.6	130	Hard	Surface and Groundwater
25	Ohio	7.6	130	Hard	Surface and Groundwater
26	South Carolina	7.6	130	Hard	Surface and Groundwater
27	Tennessee	7.6	130	Hard	Surface and Groundwater
28	West Virginia	7.6	130	Hard	Surface and Groundwater
29	Illinois	7	120	Hard	Surface (L. Michigan) and Groundwater
30	North Carolina	7	120	Hard	Surface and Groundwater
31	Pennsylvania	7	120	Hard	Surface and Groundwater
32	Virginia	7	120	Hard	Surface and Groundwater
33	Maryland	6.9	118	Moderately Hard	Surface and Groundwater
34	Kentucky	6.5	112	Moderately Hard	Surface (Ohio River) and Groundwater
35	Alaska	5.8	100	Moderately Hard	Surface and Groundwater
36	Idaho	5.8	100	Moderately Hard	Surface and Snake River Aquifer
37	Louisiana	5.8	100	Moderately Hard	Surface and Groundwater
38	New Jersey	5.8	100	Moderately Hard	Surface and Groundwater
39	Montana	5.6	95	Moderately Hard	Surface and Groundwater
40	Connecticut	4.4	75	Moderately Hard	Surface and Bedrock Wells
41	New York	4.4	75	Moderately Hard	Surface Reservoirs
42	Rhode Island	4.4	75	Moderately Hard	Surface Reservoirs
43	Mississippi	4.1	70	Moderately Hard	Groundwater (84% reliance)
44	Oregon	4.1	70	Moderately Hard	Surface (Columbia/Willamette)
45	Vermont	4.1	70	Moderately Hard	Surface and Bedrock Wells
46	Washington	4.1	70	Moderately Hard	Surface (Cedar/Tolt Rivers)
47	Hawaii	3.5	60	Moderately Hard	Groundwater (Volcanic)
48	Maine	3.5	60	Moderately Hard	Surface (Lakes) and Bedrock Wells
49	New Hampshire	3.5	60	Moderately Hard	Surface and Groundwater
50	Massachusetts	2.9	50	Slightly Hard	Surface (Quabbin Reservoir)
51	Arkansas	2.2	38	Slightly Hard	Surface (Reservoirs/Rivers)

Check Your Exact Water Hardness

Use a city reference or find your possible utility. A ZIP code is not an exact tap-water measurement.

Look Up Your ZIP Code

Frequently Asked Questions

Historical research estimates; not official state tap-water averages. These historical estimates are not verified population-weighted averages. Actual hardness varies by water system and property.