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Federal water data

County water report

Clark County Water Report

Drinking-water compliance, watershed health, monitoring records, and river conditions for Clark County, Idaho.

Water grade

F

Water score

8.7

State rank

#38

of 44

Health violations

2

EPA SDWIS, 5-year lookback

Watershed impaired

36.7%

346 water bodies assessed

Monitoring sites

37

1,531 recent measurements

Live streamflow

No gauge

BIRCH CREEK AT EIGHT-MILE CANYON RD NR RENO ID

Water at a glance

Key Water Indicators for Clark County

EPA SDWIS

Safety Grade

F

Score: 8.7 / 100

EPA SDWIS

Active Violations

2

5-year health-based lookback

EPA ATTAINS

Watershed Health

37% impaired

346 bodies assessed

USGS NWIS

Streamflow Snapshot

No gauge

BIRCH CREEK AT EIGHT-MILE CANYON RD NR RENO ID

EPA WQP

Monitoring Sites

37

1,531 recent readings

Source: EPA SDWIS · Safe Drinking Water Information System

Drinking Water Compliance

Compliance grade

F

Based on EPA SDWIS compliance history.

Water score

Higher scores indicate cleaner recent compliance records.

8.7/100

Health violations

2

Health-based violations

Violations per 100K served

391.4

Population-normalized SDWIS rate

Editorial analysis

Understanding Clark County’s Water

Drinking Water Quality Overview

EPA SDWIS

Clark County's water systems carry a failing grade, scoring 8.7 out of 100. Over the past five years, EPA SDWIS records 2 health-based violations — a small cluster that warrants attention.

Watershed Conditions

EPA ATTAINS

Under the Clean Water Act §303(d), EPA ATTAINS tracks whether waterways meet quality standards for drinking, recreation, and aquatic life (reporting cycle: 2022). A substantial 36.7% of assessed waterways are impaired (127 of 346 water bodies) across Clark County's watersheds. The leading impairment causes are temperature and sedimentation/siltation. Impairment does not mean tap water is unsafe — it measures ambient waterway conditions upstream of treatment, not finished drinking water.

Monitoring Network

EPA WQP

EPA's Water Quality Portal (WQP) aggregates monitoring data from federal, state, and tribal agencies. Clark County has moderate coverage with 37 active monitoring sites with 1,531 recent measurements on record. Predominant monitoring categories include biological, counts and biological, fish. More monitoring sites generally indicate greater scientific attention to local water conditions — and provide the baseline data that regulators use to set future impairment listings.

Editorial advisory

What the data suggests for Clark County

Water Verdict

Clark County, Idaho receives a poor water quality assessment with a grade of F and a score of 8.7 out of 100. The water supply has documented quality issues. Residents are strongly encouraged to use filtered or bottled water for drinking and to stay informed about utility improvement plans. Separately, EPA ATTAINS assessments cover 346 water bodies in the county's watershed, with 36.7% listed as impaired under the Clean Water Act — a source-water measure that is tracked independently of tap-water compliance.

Violation Context

EPA SDWIS records for Clark County, Idaho show 2 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 391.4 violations per 100,000 people served, this rate is high and signals significant water quality management issues. For independent context, 1,531 water-quality monitoring results have been recorded across the county in the EPA Water Quality Portal over the past five years.

Consumer Guidance

Drinking-water compliance in Clark County is rated Grade F, reflecting significant health-based violations in the recent reporting period. Clark County's drinking-water compliance score is 8.7 out of 100. An NSF 53 or NSF 58-certified filter is recommended for drinking and cooking water. Check the Consumer Confidence Report from your utility to identify the specific contaminants and required corrective actions — utilities are legally required to notify customers of violations. Temperature is the leading impairment cause in Clark County's watershed. With 37 active water-quality monitoring sites in Clark County, data coverage is strong. A pipeline streamflow snapshot from the BIRCH CREEK gauge is also available on this page.

Regional Context

Clark County has poorer water quality than the average county in Idaho. Its water score is 23.9 points lower than the state average, suggesting more challenges with contamination control or infrastructure than neighboring counties.

Advisory text summarizes county-level public records and is not a replacement for your utility's current Consumer Confidence Report or direct local notices.

Contaminants & Resources

Key issues flagged in Clark County's water environment

Watershed Impairment Causes (EPA ATTAINS)

  • 1

    Elevated temperature

    Impairment cause per EPA Clean Water Act §303(d) assessment

  • 2

    Sedimentation and siltation

    Impairment cause per EPA Clean Water Act §303(d) assessment

  • 3

    Combined Biota/Habitat Bioassessments

    Impairment cause per EPA Clean Water Act §303(d) assessment

Source: EPA ATTAINS · Reporting cycle 2022

Official EPA Resources for Clark County

EPA How's My Waterway

Interactive watershed health data for Clark County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Clark County

Consumer Confidence Reports (ID)

Annual water quality reports from utilities in Idaho

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

36.7%

127 of 346 assessed

Moderate concern

Top Impairment Causes

  • 1

    TEMPERATURE

  • 2

    SEDIMENTATION/SILTATION

  • 3

    COMBINED BIOTA/HABITAT BIOASSESSMENTS

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

37

Active in the past 5 years

Measurements Recorded

1.5K

1,531 total readings

Most Measured

  • Biological, Counts
  • Biological, Fish
  • Physical

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).

Free tool

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Water Cost Estimate

3

3 people  ·  ~225 gal/day

Annual Total

$558

Monthly

$47

Water Bill

$558/yr

Filter Cost

$0/yr

Safety Grade for Clark County:C — Moderate

Some violations or watershed impairment detected.

Estimates use the national average residential water rate ($0.0068/gal, EPA/AWWA 2023) and EPA WaterSense per-person consumption baseline (75 gal/person/day). Actual bills vary by utility, usage tier, and local infrastructure fees. For informational purposes only.

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Frequently Asked Questions

What is the water quality in Clark County, Idaho?
Clark County, Idaho has a drinking-water quality grade of F with a score of 8.7/100, 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 streamflow snapshots are reported separately on this page.
Are there any water violations in Clark County?
Clark 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 Clark County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 36.7% of Clark County's 346 assessed water bodies are classified as impaired (127 impaired). The top reported causes are TEMPERATURE, SEDIMENTATION/SILTATION, COMBINED BIOTA/HABITAT BIOASSESSMENTS. 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 Clark County?
EPA's Water Quality Portal records 1,531 measurements from 37 monitoring sites in Clark County over the past five years. The most frequently measured characteristic groups are Biological, Counts, Biological, Fish, Physical. 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.
How does Clark County water compare to the Idaho average?
Clark County's SDWIS water quality score of 8.7/100 is lower 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 Clark County?
Based on EPA SDWIS data, Clark County has a water quality grade of F (8.7/100). 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 Clark County have clean drinking water?
Clark County has 2 health-based drinking water violations according to EPA records. With a water quality score of 8.7/100 and grade F, 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 Clark County rank for water quality in Idaho?
Clark County ranks #38 out of 44 counties in Idaho by SDWIS water quality score (1 = best). With a score of 8.7/100, it falls in the bottom 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

Lewis County

Idaho

F

9.1

Water score

Lemhi County

Idaho

F

9.2

Water score

Franklin County

Idaho

F

8.0

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 and 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.

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 Evan Brooks, Data EditorUpdated Reviewed by Evan Brooks, Data Editor

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