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County water report

Custer County Water Report

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

Water grade

A

Water score

86.0

State rank

#2

of 44

Health violations

0

EPA SDWIS, 5-year lookback

Watershed impaired

22.9%

694 water bodies assessed

Monitoring sites

104

12,521 recent measurements

Live streamflow

415%

SALMON RIVER AB EAST FORK NR CLAYTON ID

Water at a glance

Key Water Indicators for Custer County

EPA SDWIS

Safety Grade

A

Score: 86.0 / 100

EPA SDWIS

Active Violations

0

5-year health-based lookback

EPA ATTAINS

Watershed Health

23% impaired

694 bodies assessed

USGS NWIS

Streamflow Snapshot

415% of mean

SALMON RIVER AB EAST FORK NR CLAYTON ID

EPA WQP

Monitoring Sites

104

12,521 recent readings

Source: EPA SDWIS · Safe Drinking Water Information System

Drinking Water Compliance

Compliance grade

A

Based on EPA SDWIS compliance history.

Water score

Higher scores indicate cleaner recent compliance records.

86.0/100

Health violations

0

Health-based violations

Violations per 100K served

0.0

Population-normalized SDWIS rate

Editorial analysis

Understanding Custer County’s Water

Drinking Water Quality Overview

EPA SDWIS

Custer County earns an A grade for drinking water quality, scoring 86.0 out of 100. EPA's Safe Drinking Water Information System (SDWIS) records zero health-based violations over the past five years — a strong compliance signal for a heavily urbanized county.

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 notable 22.9% of assessed waterways carry an impairment designation (159 of 694 water bodies) across Custer 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.

River & Streamflow Status

USGS NWIS

USGS NWIS gauge data (as of 2026-05-14T12:45:00.000-06:00) puts SALMON RIVER AB EAST FORK at 4.6k cfs — running significantly above its long-term average at 415% of mean flow. Streamflow is a leading indicator of drought stress, sediment load, and dilution capacity: low flows concentrate pollutants and warm water temperatures, stressing aquatic life and, in surface-water-dependent systems, the source water quality for treatment plants.

Monitoring Network

EPA WQP

EPA's Water Quality Portal (WQP) aggregates monitoring data from federal, state, and tribal agencies. Custer County has extensive coverage with 104 active monitoring sites with 12,521 recent measurements on record. Predominant monitoring categories include physical and biological, counts. 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 Custer County

Water Verdict

Custer County receives an excellent water quality assessment with a grade of A and a score of 86.0 out of 100. The water supply meets or exceeds federal safety standards, and residents can generally drink tap water with confidence.

Violation Context

Custer County has recorded zero health-based violations, indicating no recent health-based violations in the reporting period. The violation rate is zero per 100,000 people served, which is the best possible outcome.

Consumer Guidance

The EPA compliance record for Custer County shows no recent health-based violations. No health-based violations have been recorded, placing Custer County in the top tier for drinking-water safety. Custer County's drinking-water compliance score is 86.0 out of 100. As a routine precaution, requesting your utility's annual Consumer Confidence Report each July gives you a full list of detected contaminants and their treatment levels. With 104 active water-quality monitoring sites in Custer County, data coverage is strong. A pipeline streamflow snapshot from the SALMON RIVER AB EAST FORK gauge is also available on this page.

Regional Context

Custer County has better water quality than the average county in Idaho. Its water score is 53.4 points higher than the state average, indicating stronger water system performance relative to 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 Custer 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

    Flow Regime Modification

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

Source: EPA ATTAINS · Reporting cycle 2022

Official EPA Resources for Custer County

EPA How's My Waterway

Interactive watershed health data for Custer County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Custer County

Consumer Confidence Reports (ID)

Annual water quality reports from utilities in Idaho

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

22.9%

159 of 694 assessed

Some impairment

Top Impairment Causes

  • 1

    TEMPERATURE

  • 2

    SEDIMENTATION/SILTATION

  • 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

104

Active in the past 5 years

Measurements Recorded

13K

12,521 total readings

Most Measured

  • Physical
  • Biological, Counts
  • Biological, Fish

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

4,560cfs

May 14, 6:45 PM UTC

vs Long-Term Average

415%

Well above typical

Primary Streamgage

SALMON RIVER AB EAST FORK NR CLAYTON ID

USGS site
13297380
Drainage area
1,200 sq mi
Long-term mean
1,098 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; the percent-of-typical value compares the latest reading against that average.

Free tool

Estimate Your Water Costs

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 Custer County:B — Good

Minor violations; waterways mostly healthy.

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.

Try the full calculator →

Custer County has good water quality

Learn about water restrictions and conservation in your area.

Water Restrictions →

Frequently Asked Questions

What is the water quality in Custer County, Idaho?
Custer County, Idaho has a drinking-water quality grade of A with a score of 86.0/100, based on EPA SDWIS compliance data. The county has 0 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 Custer County?
Custer County has 0 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). Zero violations is an excellent record indicating consistent compliance with federal drinking water standards.
How healthy are the watersheds in Custer County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 22.9% of Custer County's 694 assessed water bodies are classified as impaired (159 impaired). The top reported causes are TEMPERATURE, SEDIMENTATION/SILTATION, 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 Custer County?
EPA's Water Quality Portal records 12,521 measurements from 104 monitoring sites in Custer County over the past five years. The most frequently measured characteristic groups are Physical, Biological, Counts, Biological, Fish. 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 Custer County right now?
Custer County's primary USGS streamgage on the SALMON RIVER AB EAST FORK has a pipeline snapshot of 4,560 cubic feet per second — 415% of the long-term mean of 1,098.33 cfs. This is well above typical — often a signal of recent precipitation or storm runoff. For the latest gauge feed, visit waterdata.usgs.gov.
How does Custer County water compare to the Idaho average?
Custer County's SDWIS water quality score of 86.0/100 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 Custer County?
Based on EPA SDWIS data, Custer County has a water quality grade of A (86.0/100). This indicates good to excellent water quality with strong SDWIS compliance. 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 Custer County have clean drinking water?
Custer County has 0 health-based drinking water violations according to EPA records. With a water quality score of 86.0/100 and grade A, the county's drinking water meets EPA standards with no recorded health violations. 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 Custer County rank for water quality in Idaho?
Custer County ranks #2 out of 44 counties in Idaho by SDWIS water quality score (1 = best). With a score of 86.0/100, 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

Adams County

Idaho

A

86.0

Water score

Oneida County

Idaho

A

86.0

Water score

Shoshone County

Idaho

A

86.0

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.

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

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