waterbycounty
Compiled federal source snapshot

New Hampshire Water Quality

Drinking water data for all 10 counties.

Avg SDWIS Compliance Index

35.9

Most Common Five-Year SDWIS Compliance Band

F

Counties with Data

10

of 10 total

County water atlas

New Hampshire water signals by county

A state-level 2.5D view across drinking-water compliance, watershed impairment, monitoring density, and streamflow snapshot context. Pin any county, switch layers, then use the lens controls to compare index ranges, recorded violation rates, or impaired watersheds without leaving the page.

Counties

10

Avg SDWIS index

35.9

Watersheds

3

ATTAINS counties

Monitoring

10

9 fresh USGS snapshots

State atlas layers combine EPA SDWIS health-based violations, EPA ATTAINS 303(d) impairment assessments, EPA Water Quality Portal monitoring sites, and representative USGS NWIS streamflow gauges. Streamflow values appear only for fresh pipeline snapshots, not as a continuously updated stream. County pages include the observation time and year.

Prepared by ByCounty Editorial TeamPublished by WaterByCounty

Multi-source coverage in New Hampshire

Beyond Drinking Water

EPA SDWIS

10/ 10

counties with drinking-water compliance data

315 health violations statewide (5yr)

EPA ATTAINS

100.0%

avg impaired across 3 counties

3 of 3 assessed bodies impaired

EPA WQP

2,449

monitoring sites across 10 counties

202,810 total readings (5yr window)

USGS NWIS

9

counties with a fresh pipeline snapshot

0 above9 below

State atlas notes

What stands out in New Hampshire

County water quality is not one number. The strongest read comes from comparing drinking-water compliance against watershed impairment, monitoring density, and streamflow context. Use these signals as a starting point, then open any county profile for source-level detail.

Compliance spread

Cheshire County has the highest value in the published state SDWIS Compliance Index table at 60.3/100, while Carroll County has the lowest at 7.2/100. That is a 53.1 point gap inside one state.

Zero health violations

0

3+ health violations

7

Watershed pressure

The atlas impairment layer points to counties where assessed water bodies are most likely to miss state quality standards. Assessment density varies, so compare the percentage with the number of assessed bodies on the county page.

Cheshire County100.0%Hillsborough County100.0%Sullivan County100.0%

Monitoring hubs

Rockingham County455 sitesMerrimack County384 sitesCheshire County296 sites

Lowest flow reads

Cheshire County25%Sullivan County26%Coos County27%

Highest fresh streamflow pipeline snapshots: Belknap County (69%, observation 2026), Strafford County (68%, observation 2026), Hillsborough County (60%, observation 2026). These are source-data observations, not household tap-water conclusions.

All New Hampshire Counties

CountySDWIS Compliance Index
Cheshire County60.3
Sullivan County60.3
Coos County51.6
Hillsborough County45.1
Strafford County38.9
Rockingham County31.5
Grafton County28.3
Merrimack County22.4
Belknap County13.3
Carroll County7.2

Frequently Asked Questions

Which New Hampshire county has the highest SDWIS Compliance Index?
Cheshire County has the highest SDWIS Compliance Index in the published New Hampshire cohort at 60.3/100. This WaterByCounty relative comparison is not an EPA score and does not establish current conditions for a utility or address.
What does the Five-Year SDWIS Compliance Band mean?
The band is derived only from each county aggregation's recorded health-violation rate per 100,000 people served for the stated five-year source window. It is separate from the relative SDWIS Compliance Index and is not a current determination for a specific utility or address.
What does EPA ATTAINS report across New Hampshire?
Across 3 published New Hampshire county records with EPA ATTAINS data, 3 of 3 assessed water bodies are listed as impaired. This is a watershed assessment and does not describe finished household tap water.
Which USGS streamflow records are shown across New Hampshire?
WaterByCounty has 9 fresh USGS pipeline snapshots in the published New Hampshire cohort. Each county page shows its observation timestamp and year. A pipeline snapshot is not a continuously updated reading or a tap-water safety measure.
Where can New Hampshire residents find current official information?
Review the applicable utility's Consumer Confidence Report, active notices, and the state drinking-water agency. WaterByCounty's county-level historical aggregations do not establish the current status of a specific utility, address, private well, or household plumbing system.
What does Water Quality Portal monitoring volume show in New Hampshire?
The published county records contain 202,810 results from 2,449 monitoring locations in the site's five-year aggregation. Monitoring volume does not by itself indicate better or worse water quality.

Data Sources

Drinking-water compliance data from the EPA Safe Drinking Water Information System (SDWIS) via the ECHO enforcement database. The WaterByCounty SDWIS Compliance Index reflects the recorded rate and is not an EPA score.

Disclaimer: This data is informational only. It is not health, legal, or professional advice. For concerns about your specific water supply, contact your local water utility.

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