waterbycounty
EPA SDWIS

Coos County Water Quality

Coos County, New Hampshire

Water Grade

D

Water Score

49.9

Violations

4

State Rank

#3

of 10 (1 = best)

EPA SDWIS Compliance

Drinking Water Quality

Water Quality Grade

D

Based on EPA compliance history and violation data

Water Score

49.9/100

Higher = better quality

Health Violations

4

Health-based violations

Violation Rate

16.8%

Systems with violations

Water Advisory: Coos County

Water Verdict

Coos County receives a below-average water quality assessment with a grade of D and a score of 49.9 out of 100. Residents should review their utility's Consumer Confidence Report and may want to consider additional water filtration for drinking.

Violation Context

Coos County has recorded 4 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 16.8 violations per 1,000 residents, this rate is high and signals significant water quality management issues.

Consumer Guidance

Residents of Coos County are advised to use filtered or bottled water for drinking and cooking until water quality improves. A reverse-osmosis or activated-carbon filter certified to remove the contaminants listed in the utility's Consumer Confidence Report is recommended. With 4 recorded health violations, staying informed about utility communications and boil-water notices is especially important. For long-term peace of mind, request your utility's latest Consumer Confidence Report and consider independent water testing if you have specific health concerns.

Regional Context

Coos County has better water quality than the average county in New Hampshire. Its water score is 16.7 points higher than the state average, indicating stronger water system performance relative to neighboring counties.

Past 5 years

Water Quality Monitoring

Monitoring Sites

82

Active in the past 5 years

Measurements Recorded

4.4K

4,367 total readings

Most Measured

  • Physical
  • Nutrient
  • Microbiological

Categories measured most frequently

Data from the EPA Water Quality Portal (WQP), aggregating monitoring records from federal, state, and tribal sources. Each measurement represents a single sample analyzed for a specific characteristic (e.g., E. coli, pH, dissolved oxygen, nitrogen).

Live USGS Streamgage

River & Stream Conditions

Current Discharge

3,260cfs

May 14, 6:15 PM UTC

vs Long-Term Average

110%

Above typical

Primary Streamgage

CONNECTICUT RIVER NEAR DALTON, NH

USGS site
01131500
Drainage area
1,514 sq mi
Long-term mean
2,962 cfs

One representative streamgage (the one with the largest drainage area in the county). Many counties have multiple gauges — this view summarizes the primary one. The long-term mean is the full-record annual average; "% of typical" compares the latest reading against that average.

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Frequently Asked Questions

What is the water quality in Coos County, New Hampshire?
Coos County, New Hampshire has a drinking-water quality grade of D with a score of 49.9/100, based on EPA SDWIS compliance data. The county has 4 health-based drinking water violations over the past 5 years. Watershed health, monitoring records, and live streamflow are reported separately on this page.
Are there any water violations in Coos County?
Coos County has 4 health-based drinking water violations recorded by the EPA over the past 5 years. Health-based violations indicate instances where contaminant levels exceeded EPA Maximum Contaminant Levels (MCLs). Violations may have been resolved — check with your local water utility for current status.
How much water-quality monitoring happens in Coos County?
EPA's Water Quality Portal records 4,367 measurements from 82 monitoring sites in Coos County over the past five years. The most frequently measured characteristic groups are Physical, Nutrient, Microbiological. Each measurement is a single sample analyzed for one characteristic (E. coli, pH, dissolved oxygen, etc.). High monitoring density means more scientific evidence behind any reported signal — it does not by itself indicate water quality.
What's happening with rivers in Coos County right now?
Coos County's primary USGS streamgage on the CONNECTICUT RIVER is currently reading 3,260 cubic feet per second — 110% of the long-term mean of 2,961.64 cfs. Flow is within typical range for this gauge. For genuine real-time data, visit waterdata.usgs.gov.
How does Coos County water compare to the New Hampshire average?
Coos County's SDWIS water quality score of 49.9/100 is higher than the New Hampshire state average of 33.2. The average water quality grade across New Hampshire is F, based on data from 10 counties with available SDWIS data.
Is tap water safe to drink in Coos County?
Based on EPA SDWIS data, Coos County has a water quality grade of D (49.9/100). This indicates below-average compliance with significant violations. Residents may want to consider home water filtration or independent testing. The grade speaks to the public water system, not the watershed — for watershed-level concerns, see the Watershed Health zone. For the most up-to-date information, contact your local water utility or review your Consumer Confidence Report (CCR).
Does Coos County have clean drinking water?
Coos County has 4 health-based drinking water violations according to EPA records. With a water quality score of 49.9/100 and grade D, the county's drinking water has had some compliance issues but continues to be monitored. Note: drinking-water compliance speaks to the public water system, not necessarily to the watershed itself — check the Watershed Health zone for ATTAINS §303(d) data.
How does Coos County rank for water quality in New Hampshire?
Coos County ranks #3 out of 10 counties in New Hampshire by SDWIS water quality score (1 = best). With a score of 49.9/100, it falls in the top third of counties statewide. The ranking reflects EPA SDWIS compliance only — not watershed impairment, monitoring density, or streamflow, which are tracked separately on this page.

Counties with Similar Water Quality

Cheshire County

New Hampshire

C

51.2

Water score

Sullivan County

New Hampshire

C

57.8

Water score

Hillsborough County

New Hampshire

D

41.5

Water score

Data Sources

Drinking-water compliance data from the EPA Safe Drinking Water Information System (SDWIS) via the ECHO enforcement database. Scores reflect compliance history and health-based violation counts.

Water-quality monitoring counts from the EPA Water Quality Portal (WQP) — federated USGS, EPA, and state agency sampling records over a rolling 5-year window.

Live streamflow from the USGS National Water Information System (NWIS) — continuous discharge measurements from the largest-drainage gauge in each county, compared against the full-record long-term annual mean.

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.

By Logan Johnson, Founder & Data EditorUpdated Reviewed by Logan Johnson, Founder & Data Editor

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