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EPA SDWIS

Nez Perce County Water Quality

Nez Perce County, Idaho

Water Grade

C

Water Score

61.5

Violations

2

State Rank

#6

of 44 (1 = best)

EPA SDWIS Compliance

Drinking Water Quality

Water Quality Grade

C

Based on EPA compliance history and violation data

Water Score

61.5/100

Higher = better quality

Health Violations

2

Health-based violations

Violation Rate

5.4%

Systems with violations

Water Advisory: Nez Perce County

Water Verdict

Nez Perce County receives a fair water quality assessment with a grade of C and a score of 61.5 out of 100. The water supply meets baseline federal standards, but there may be periods of elevated contaminant levels or infrastructure concerns worth monitoring.

Violation Context

Nez Perce County has recorded 2 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 5.4 violations per 1,000 residents, this rate is moderate and suggests recurring water quality challenges.

Consumer Guidance

Tap water in Nez Perce County meets baseline standards, but residents who are immunocompromised or have young children may want to use an NSF-certified water filter as a precaution. With 2 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

Nez Perce County has better water quality than the average county in Idaho. Its water score is 28.9 points higher than the state average, indicating stronger water system performance relative to neighboring counties.

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

36.8%

179 of 486 assessed

Moderate concern

Top Impairment Causes

  • 1

    TEMPERATURE

  • 2

    PHYSICAL SUBSTRATE HABITAT ALTERATIONS

  • 3

    FLOW REGIME MODIFICATION

Source: EPA ATTAINS · Reporting cycle 2022

Impairment is determined under the Clean Water Act §303(d): a water body is impaired when it fails to meet state-defined quality standards for designated uses (drinking, recreation, aquatic life). Assessment coverage varies by state — counties without assessed water bodies are not shown.

Past 5 years

Water Quality Monitoring

Monitoring Sites

19

Active in the past 5 years

Measurements Recorded

2.4K

2,442 total readings

Most Measured

  • Physical
  • Nutrient
  • Inorganics, Minor, Metals

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

35.8Kcfs

May 14, 6:00 PM UTC

vs Long-Term Average

241%

Well above typical

Primary Streamgage

CLEARWATER RIVER AT SPALDING ID

USGS site
13342500
Drainage area
9,283 sq mi
Long-term mean
14.9K 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 Nez Perce County, Idaho?
Nez Perce County, Idaho has a drinking-water quality grade of C with a score of 61.5/100, based on EPA SDWIS compliance data. The county has 2 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 Nez Perce County?
Nez Perce County has 2 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 healthy are the watersheds in Nez Perce County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 36.8% of Nez Perce County's 486 assessed water bodies are classified as impaired (179 impaired). The top reported causes are TEMPERATURE, PHYSICAL SUBSTRATE HABITAT ALTERATIONS, FLOW REGIME MODIFICATION. Impairment means the water body fails to meet state quality standards for at least one designated use — drinking water source, recreation, aquatic life, or fish consumption. Note: watershed impairment doesn't always translate to tap-water issues; treatment plants can remove most regulated contaminants.
How much water-quality monitoring happens in Nez Perce County?
EPA's Water Quality Portal records 2,442 measurements from 19 monitoring sites in Nez Perce County over the past five years. The most frequently measured characteristic groups are Physical, Nutrient, Inorganics, Minor, Metals. 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 Nez Perce County right now?
Nez Perce County's primary USGS streamgage on the CLEARWATER RIVER is currently reading 35,800 cubic feet per second — 241% of the long-term mean of 14,856.89 cfs. This is well above typical — often a signal of recent precipitation or storm runoff. For genuine real-time data, visit waterdata.usgs.gov.
How does Nez Perce County water compare to the Idaho average?
Nez Perce County's SDWIS water quality score of 61.5/100 is higher than the Idaho state average of 32.6. The average water quality grade across Idaho is F, based on data from 44 counties with available SDWIS data.
Is tap water safe to drink in Nez Perce County?
Based on EPA SDWIS data, Nez Perce County has a water quality grade of C (61.5/100). This indicates moderate compliance. Some violations have been recorded but overall standards are maintained. 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 Nez Perce County have clean drinking water?
Nez Perce County has 2 health-based drinking water violations according to EPA records. With a water quality score of 61.5/100 and grade C, 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 Nez Perce County rank for water quality in Idaho?
Nez Perce County ranks #6 out of 44 counties in Idaho by SDWIS water quality score (1 = best). With a score of 61.5/100, 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

Ada County

Idaho

C

55.6

Water score

Bannock County

Idaho

C

53.8

Water score

Twin Falls County

Idaho

C

52.8

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.

Watershed health and impaired-waterway data from the EPA ATTAINS Clean Water Act §303(d) assessments — state-reported, EPA-finalized.

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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