countyscore

Best Water Quality Counties in Iowa

EPA drinking water health violations and safety grades Compare rankings across all 99 counties.

Average Water Quality Score
72/100
Top County
Adair County
Counties Ranked
99

Top 10

#1
Adair County
IA
86/100
#2
Adams County
IA
86/100
#3
Allamakee County
IA
86/100
#4
Appanoose County
IA
86/100
#5
Audubon County
IA
86/100
#6
Black Hawk County
IA
86/100
#7
Bremer County
IA
86/100
#8
Buchanan County
IA
86/100
#9
Buena Vista County
IA
86/100
#10
Cerro Gordo County
IA
86/100

All Iowa Counties Ranked

#CountyWater Quality ScoreOverall Score
1Adair County, IA
86
62.5
2Adams County, IA
86
61.1
3Allamakee County, IA
86
60.2
4Appanoose County, IA
86
48.6
5Audubon County, IA
86
59.7
6Black Hawk County, IA
86
40.7
7Bremer County, IA
86
58.6
8Buchanan County, IA
86
62.4
9Buena Vista County, IA
86
46.7
10Cerro Gordo County, IA
86
42.5
11Cherokee County, IA
86
66.8
12Clay County, IA
86
59.7
13Clayton County, IA
86
59.9
14Clinton County, IA
86
38.7
15Crawford County, IA
86
55.3
16Dallas County, IA
86
42
17Davis County, IA
86
56
18Delaware County, IA
86
60.2
19Emmet County, IA
86
61.6
20Fayette County, IA
86
57
21Floyd County, IA
86
56.7
22Franklin County, IA
86
65.5
23Fremont County, IA
86
58.7
24Greene County, IA
86
58.4
25Grundy County, IA
86
69.1
26Hamilton County, IA
86
57.6
27Hardin County, IA
86
48.1
28Harrison County, IA
86
58.5
29Henry County, IA
86
52.5
30Howard County, IA
86
68.1
31Humboldt County, IA
86
63.4
32Ida County, IA
86
71.2
33Jackson County, IA
86
55.6
34Jasper County, IA
86
54.1
35Jefferson County, IA
86
48.4
36Keokuk County, IA
86
58.5
37Kossuth County, IA
86
66.6
38Lee County, IA
86
42.8
39Louisa County, IA
86
61.3
40Lucas County, IA
86
55.8
41Lyon County, IA
86
65.1
42Madison County, IA
86
58.6
43Mahaska County, IA
86
51.4
44Marion County, IA
86
59.2
45Marshall County, IA
86
42
46Mitchell County, IA
86
66.2
47Monona County, IA
86
59.3
48Monroe County, IA
86
59.1
49Montgomery County, IA
86
53.5
50Muscatine County, IA
86
41.3
51O'Brien County, IA
86
61.5
52Osceola County, IA
86
65.3
53Plymouth County, IA
86
47.3
54Pottawattamie County, IA
86
36.1
55Ringgold County, IA
86
60.8
56Shelby County, IA
86
66.5
57Sioux County, IA
86
59.1
58Tama County, IA
86
56.6
59Taylor County, IA
86
64.2
60Union County, IA
86
53.6
61Van Buren County, IA
86
60.6
62Wapello County, IA
86
33.1
63Warren County, IA
86
51.7
64Washington County, IA
86
51.6
65Wayne County, IA
86
62.9
66Winnebago County, IA
86
68.8
67Winneshiek County, IA
86
67.9
68Worth County, IA
86
70.4
69Wright County, IA
86
59.7
70Polk County, IA
69.8
36.6
71Linn County, IA
69
40.7
72Scott County, IA
68.2
37.2
73Woodbury County, IA
67.8
50.9
74Dubuque County, IA
67.1
45.4
75Story County, IA
66.8
46.9
76Des Moines County, IA
66
34.7
77Page County, IA
59.4
52.7
78Dickinson County, IA
46.3
59.1
79Jones County, IA
44.5
60.7
80Chickasaw County, IA
41.8
66.7
81Boone County, IA
41.1
57.8
82Cedar County, IA
39.4
58
83Johnson County, IA
37.9
41.1
84Pocahontas County, IA
37.5
65.2
85Hancock County, IA
36.4
61.6
86Benton County, IA
36.1
56
87Webster County, IA
35.8
41.6
88Clarke County, IA
34.5
43.7
89Butler County, IA
32.4
62.1
90Guthrie County, IA
28.6
60.2
91Cass County, IA
27.6
42.7
92Carroll County, IA
17.6
61.5
93Sac County, IA
17.6
63.9
94Poweshiek County, IA
13.6
46.8
95Palo Alto County, IA
13.1
62.4
96Iowa County, IA
11.3
56.6
97Calhoun County, IA
11.2
65.9
98Decatur County, IA
11.1
59.4
99Mills County, IA
10.8
46.7

Data Source

Water Quality data from WaterByCounty. See full details at WaterByCounty. Data updated February 2026.