countyscore

Best Water Quality Counties in California

EPA drinking water health violations and safety grades Compare rankings across all 58 counties.

Average Water Quality Score
45/100
Top County
San Francisco County
Counties Ranked
58

Top 10

#1
San Francisco County
CA
86/100
#2
Alameda County
CA
72/100
#3
Orange County
CA
72/100
#4
Placer County
CA
70/100
#5
Sacramento County
CA
69/100
#6
Santa Clara County
CA
68/100
#7
San Mateo County
CA
67/100
#8
Marin County
CA
67/100
#9
Los Angeles County
CA
67/100
#10
Riverside County
CA
65/100

All California Counties Ranked

#CountyWater Quality ScoreOverall Score
1San Francisco County, CA
86
43.6
2Alameda County, CA
71.9
40.6
3Orange County, CA
71.5
44.3
4Placer County, CA
69.8
46.5
5Sacramento County, CA
69
38.3
6Santa Clara County, CA
67.5
42.2
7San Mateo County, CA
67.1
47.6
8Marin County, CA
66.8
47.4
9Los Angeles County, CA
66.5
36.9
10Riverside County, CA
65.1
37.2
11Ventura County, CA
63
44.3
12Glenn County, CA
61.7
41.8
13Yuba County, CA
59.8
37.7
14Santa Barbara County, CA
58.9
43
15Nevada County, CA
58.7
45.2
16Butte County, CA
57.2
39.3
17El Dorado County, CA
57.1
49.8
18Humboldt County, CA
54.8
40
19Lassen County, CA
54.6
40.4
20San Diego County, CA
54.6
42.3
21Fresno County, CA
52.5
33
22San Bernardino County, CA
52.3
33.7
23Santa Cruz County, CA
50.6
41.6
24Solano County, CA
49.9
36.4
25Shasta County, CA
48.5
52.3
26Imperial County, CA
48.3
33.7
27Sutter County, CA
47.2
35
28Contra Costa County, CA
47
40.1
29Yolo County, CA
45.6
38
30Sonoma County, CA
45.1
44.8
31San Joaquin County, CA
45
33.1
32Merced County, CA
43.2
35.3
33Stanislaus County, CA
42.9
35.6
34Calaveras County, CA
40.6
43
35Del Norte County, CA
40.5
39.9
36San Benito County, CA
38.6
43.3
37Kings County, CA
35.5
38.2
38Mendocino County, CA
35.2
44.1
39Amador County, CA
34.8
41.8
40Tuolumne County, CA
34
41.7
41Napa County, CA
33.4
43.6
42Modoc County, CA
31.1
49.7
43Kern County, CA
30
27.8
44Mono County, CA
28
38.5
45Monterey County, CA
28
39
46Siskiyou County, CA
27.9
37.9
47Lake County, CA
27.8
31.6
48Plumas County, CA
27.8
41
49Inyo County, CA
27.5
41.1
50Sierra County, CA
26.1
52.4
51Mariposa County, CA
25
43.9
52Tulare County, CA
23.4
35.2
53San Luis Obispo County, CA
21.3
42.9
54Trinity County, CA
18.5
48.3
55Tehama County, CA
15.7
36.7
56Alpine County, CA
13.8
51.2
57Colusa County, CA
13.1
41.8
58Madera County, CA
8.8
35.5

Data Source

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