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County water report

Jefferson County Water Report

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

Water grade

F

Water score

17.4

State rank

#28

of 44

Health violations

15

EPA SDWIS, 5-year lookback

Watershed impaired

41.2%

330 water bodies assessed

Monitoring sites

8

1,015 recent measurements

Live streamflow

151%

SNAKE RIVER AT LORENZO ID

Water at a glance

Key Water Indicators for Jefferson County

EPA SDWIS

Safety Grade

F

Score: 17.4 / 100

EPA SDWIS

Active Violations

15

5-year health-based lookback

EPA ATTAINS

Watershed Health

41% impaired

330 bodies assessed

USGS NWIS

Streamflow Snapshot

151% of mean

SNAKE RIVER AT LORENZO ID

EPA WQP

Monitoring Sites

8

1,015 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.

17.4/100

Health violations

15

Health-based violations

Violations per 100K served

159.3

Population-normalized SDWIS rate

Editorial analysis

Understanding Jefferson County’s Water

Drinking Water Quality Overview

EPA SDWIS

Jefferson County's water systems carry a failing grade, scoring 17.4 out of 100. Over the past five years, EPA SDWIS records 15 health-based violations — a pattern that public water utilities are required to disclose and correct.

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 41.2% of assessed waterways are impaired (136 of 330 water bodies) across Jefferson 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 2026-05-14T12:15:00.000-06:00) puts SNAKE RIVER at 6.0k cfs — running significantly above its long-term average at 151% 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. Jefferson County has limited coverage with 8 active monitoring sites with 1,015 recent measurements on record. Predominant monitoring categories include organics, other and nutrient. 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 Jefferson County

Water Verdict

Jefferson County, Idaho receives a poor water quality assessment with a grade of F and a score of 17.4 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 330 water bodies in the county's watershed, with 41.2% listed as impaired under the Clean Water Act — a source-water measure that is tracked independently of tap-water compliance. At the most recent USGS reading, local streamflow was running above its historical mean at 150.5%.

Violation Context

EPA SDWIS records for Jefferson County, Idaho show 15 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 159.3 violations per 100,000 people served, this rate is high and signals significant water quality management issues. For independent context, 1,015 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 Jefferson County is rated Grade F, reflecting significant health-based violations in the recent reporting period. Jefferson County's drinking-water compliance score is 17.4 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 Jefferson County's watershed. There are 8 active water-quality monitoring sites in Jefferson County. A pipeline streamflow snapshot from the SNAKE RIVER gauge is also available on this page.

Regional Context

Jefferson County has poorer water quality than the average county in Idaho. Its water score is 15.2 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 Jefferson 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

    E. coli (bacteria)

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

Source: EPA ATTAINS · Reporting cycle 2022

Official EPA Resources for Jefferson County

EPA How's My Waterway

Interactive watershed health data for Jefferson County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Jefferson County

Consumer Confidence Reports (ID)

Annual water quality reports from utilities in Idaho

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

41.2%

136 of 330 assessed

Moderate concern

Top Impairment Causes

  • 1

    TEMPERATURE

  • 2

    SEDIMENTATION/SILTATION

  • 3

    ESCHERICHIA COLI (E. COLI)

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

8

Active in the past 5 years

Measurements Recorded

1.0K

1,015 total readings

Most Measured

  • Organics, Other
  • Nutrient
  • 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).

Live USGS Streamgage

River & Stream Conditions

Current Discharge

6,040cfs

May 14, 6:15 PM UTC

vs Long-Term Average

151%

Well above typical

Primary Streamgage

SNAKE RIVER AT LORENZO ID

USGS site
13038500
Drainage area
5,810 sq mi
Long-term mean
4,014 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.

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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 Jefferson 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 Jefferson County, Idaho?
Jefferson County, Idaho has a drinking-water quality grade of F with a score of 17.4/100, based on EPA SDWIS compliance data. The county has 15 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 Jefferson County?
Jefferson County has 15 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 Jefferson County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 41.2% of Jefferson County's 330 assessed water bodies are classified as impaired (136 impaired). The top reported causes are TEMPERATURE, SEDIMENTATION/SILTATION, ESCHERICHIA COLI (E. COLI). 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 Jefferson County?
EPA's Water Quality Portal records 1,015 measurements from 8 monitoring sites in Jefferson County over the past five years. The most frequently measured characteristic groups are Organics, Other, Nutrient, 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.
What's happening with rivers in Jefferson County right now?
Jefferson County's primary USGS streamgage on the SNAKE RIVER has a pipeline snapshot of 6,040 cubic feet per second — 151% of the long-term mean of 4,013.67 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 Jefferson County water compare to the Idaho average?
Jefferson County's SDWIS water quality score of 17.4/100 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 Jefferson County?
Based on EPA SDWIS data, Jefferson County has a water quality grade of F (17.4/100). 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).
Why does Jefferson County have so many water violations?
Jefferson County has 15 health-based drinking water violations on record from the EPA SDWIS database. A higher violation count can result from aging infrastructure, underfunded water utilities, agricultural runoff contamination, or industrial pollution. Counties with more water systems may also see more violations simply due to scale. Residents concerned about water quality should consider independent water testing and home filtration systems.
How does Jefferson County rank for water quality in Idaho?
Jefferson County ranks #28 out of 44 counties in Idaho by SDWIS water quality score (1 = best). With a score of 17.4/100, it falls in the middle 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

Madison County

Idaho

F

17.5

Water score

Blaine County

Idaho

F

18.1

Water score

Payette County

Idaho

F

16.4

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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