countyscore

Best Water Quality Counties in New Hampshire

EPA drinking water health violations and safety grades Compare rankings across all 10 counties.

Average Water Quality Score
33/100
Top County
Sullivan County
Counties Ranked
10

Top 10

#1
Sullivan County
NH
58/100
#2
Cheshire County
NH
51/100
#3
Coos County
NH
50/100
#4
Hillsborough County
NH
42/100
#5
Strafford County
NH
36/100
#6
Grafton County
NH
27/100
#7
Rockingham County
NH
26/100
#8
Merrimack County
NH
21/100
#9
Belknap County
NH
14/100
#10
Carroll County
NH
8/100

All New Hampshire Counties Ranked

#CountyWater Quality ScoreOverall Score
1Sullivan County, NH
57.8
42.8
2Cheshire County, NH
51.2
43.4
3Coos County, NH
49.9
41.2
4Hillsborough County, NH
41.5
39.3
5Strafford County, NH
35.9
40.2
6Grafton County, NH
27.4
44.5
7Rockingham County, NH
26.4
48.9
8Merrimack County, NH
20.5
43.6
9Belknap County, NH
13.5
38.3
10Carroll County, NH
7.5
49

Data Source

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