Iowa water hardness, by utility.

21 Iowa utilities serving 293,184 people as they report it, from the state’s own results. Hardness is the calcium and magnesium in water; EPA sets no limit for it.

The short answer

Very hard water reaches the most people here: 18 utilities serving 289,612. Another 2 utilities, serving 1,979, have water in more than one band.

The largest, Iowa - American WTR Co - Davenport, is very hard, 239 mg/L (14 grains per gallon).

Very hard

Above 180 mg/L (10.5 grains per gallon). 18 utilities serving 289,612 people, largest first.

Iowa utilities: very hard water
Utility	Based in	Serves	Hardness, mg/L	Grains per gallon
Iowa - American WTR Co - Davenport	Davenport	147,720	239	14
Sioux City Water Supply	Sioux City	85,791	581	34
Iowa - American WTR Co - Clinton District	Clinton	24,769	287	16.8
Tiffin Water Supply	Tiffin	7,577	560	32.7
Osceola Rural Water System - North	May City	7,002	404	23.6
Huxley Waterworks Dept	Huxley	4,244	352	20.6
Onawa Municipal Water Plant	Onawa	2,906	480	28.1
Rock Rapids Municipal Water Works	Rock Rapids	2,611	444	26
Jesup Municipal Water Supply	Jesup	2,508	295	17.3
Osceola Rural Water System - South	Sutherland	2,112	462	27
Dunkerton Muni Water Supply	Dunkerton	842	220	12.9
Ventura Water Works	Ventura	717	340	19.9
Steamboat Rock Water Dept	Steamboat Rock	264	376	22
Iowa - American Water - Dixon	Dixon	204	316	18.5
Hastings Water Supply	Hastings	152	295	17.3
Oyens Water Supply	Oyens	92	336	19.6
Beyonder Getaway at Sleepy Hollow	Oxford	70	480	28.1
Rodman Water System	Rodman	31	540	31.6

Hard

121 to 180 mg/L (7.1 to 10.5 grains per gallon). 1 utility serving 1,593 people, largest first.

Iowa utilities: hard water
Utility	Based in	Serves	Hardness, mg/L	Grains per gallon
Guthrie Center Muni Water Work	Guthrie Center	1,593	178	10.4

Varies

Water in more than one band, depending on where or when it was sampled: each is given as its range, softest to hardest, and its report says more. 2 utilities serving 1,979 people, largest first.

Iowa utilities: varies water
Utility	Based in	Serves	Hardness, mg/L	Grains per gallon
Sanborn Water Supply	Sanborn	1,392	115 to 129	6.7 to 7.5
Early Municipal Water Supply	Early	587	72 to 771	4.2 to 45.1

Source: Iowa Department of Natural Resources, Water Supply Programs, 21 utilities, results from Jan. 11, 2016 to Nov. 3, 2025, read Oct. 10, 2026. Each sampling point is taken at its median; a figure is typical where every point falls in one band.

Bands are the U.S. Geological Survey’s, at 17.1 mg/L to the grain. People served is what each utility reports; where one sells water to another, the same people can be counted twice. How hardness is measured here.

Very hard

Hard

Varies

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