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Federal water data

County water report

Twin Falls County Water Report

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

Water grade

C

Water score

52.8

State rank

#9

of 44

Health violations

9

EPA SDWIS, 5-year lookback

Watershed impaired

50.6%

255 water bodies assessed

Monitoring sites

52

49,968 recent measurements

Live streamflow

112%

SNAKE RIVER NR BUHL ID

Water at a glance

Key Water Indicators for Twin Falls County

EPA SDWIS

Safety Grade

C

Score: 52.8 / 100

EPA SDWIS

Active Violations

9

5-year health-based lookback

EPA ATTAINS

Watershed Health

51% impaired

255 bodies assessed

USGS NWIS

Streamflow Snapshot

112% of mean

SNAKE RIVER NR BUHL ID

EPA WQP

Monitoring Sites

52

49,968 recent readings

Source: EPA SDWIS · Safe Drinking Water Information System

Drinking Water Compliance

Compliance grade

C

Based on EPA SDWIS compliance history.

Water score

Higher scores indicate cleaner recent compliance records.

52.8/100

Health violations

9

Health-based violations

Violations per 100K served

12.6

Population-normalized SDWIS rate

Editorial analysis

Understanding Twin Falls County’s Water

Drinking Water Quality Overview

EPA SDWIS

Twin Falls County's drinking water earned a C grade, scoring 52.8 out of 100. Over the past five years, EPA SDWIS records 9 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 50.6% of assessed waterways are impaired (129 of 255 water bodies) across Twin Falls County's watersheds. The leading impairment causes are phosphorus, total and temperature. 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 5.1k cfs — flowing above its historical average at 112% of mean. 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. Twin Falls County has extensive coverage with 52 active monitoring sites with 49,968 recent measurements on record. Predominant monitoring categories include organics, pesticide 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 Twin Falls County

Water Verdict

Twin Falls County receives a below-average water quality assessment with a grade of C and a score of 52.8 out of 100. Residents should review their utility's Consumer Confidence Report and may want to consider additional water filtration for drinking.

Violation Context

Twin Falls County has recorded 9 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 12.6 violations per 100,000 people served, this rate is high and signals significant water quality management issues.

Consumer Guidance

Tap water in Twin Falls County meets baseline standards but the compliance record shows room for improvement, with a Grade C rating. Twin Falls County's drinking-water compliance score is 52.8 out of 100. The violation rate for Twin Falls County is 12.6 per 100,000 people served. Residents who are immunocompromised, pregnant, or have young children may benefit from using an NSF 53-certified filter. Contacting your local utility for the current Consumer Confidence Report will confirm which specific violations were recorded and whether they have been resolved. Phosphorus, Total is the leading impairment cause in Twin Falls County's watershed. With 52 active water-quality monitoring sites in Twin Falls County, data coverage is strong. A pipeline streamflow snapshot from the SNAKE RIVER gauge is also available on this page.

Regional Context

Twin Falls County has better water quality than the average county in Idaho. Its water score is 20.2 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 Twin Falls County's water environment

Watershed Impairment Causes (EPA ATTAINS)

  • 1

    Phosphorus (excess nutrients)

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

  • 2

    Elevated temperature

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

  • 3

    Total Suspended Solids (Tss)

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

Source: EPA ATTAINS · Reporting cycle 2022

Official EPA Resources for Twin Falls County

EPA How's My Waterway

Interactive watershed health data for Twin Falls County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Twin Falls County

Consumer Confidence Reports (ID)

Annual water quality reports from utilities in Idaho

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

50.6%

129 of 255 assessed

Moderate concern

Top Impairment Causes

  • 1

    PHOSPHORUS, TOTAL

  • 2

    TEMPERATURE

  • 3

    TOTAL SUSPENDED SOLIDS (TSS)

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

52

Active in the past 5 years

Measurements Recorded

50K

49,968 total readings

Most Measured

  • Organics, Pesticide
  • 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

5,140cfs

May 14, 6:15 PM UTC

vs Long-Term Average

112%

Above typical

Primary Streamgage

SNAKE RIVER NR BUHL ID

USGS site
13094000
Drainage area
22,990 sq mi
Long-term mean
4,598 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 Twin Falls County:D — Poor

Elevated violations or significant watershed impairment.

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 Twin Falls County, Idaho?
Twin Falls County, Idaho has a drinking-water quality grade of C with a score of 52.8/100, based on EPA SDWIS compliance data. The county has 9 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 Twin Falls County?
Twin Falls County has 9 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 Twin Falls County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 50.6% of Twin Falls County's 255 assessed water bodies are classified as impaired (129 impaired). The top reported causes are PHOSPHORUS, TOTAL, TEMPERATURE, TOTAL SUSPENDED SOLIDS (TSS). 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 Twin Falls County?
EPA's Water Quality Portal records 49,968 measurements from 52 monitoring sites in Twin Falls County over the past five years. The most frequently measured characteristic groups are Organics, Pesticide, 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 Twin Falls County right now?
Twin Falls County's primary USGS streamgage on the SNAKE RIVER has a pipeline snapshot of 5,140 cubic feet per second — 112% of the long-term mean of 4,597.71 cfs. Flow is within typical range for this gauge. For the latest gauge feed, visit waterdata.usgs.gov.
How does Twin Falls County water compare to the Idaho average?
Twin Falls County's SDWIS water quality score of 52.8/100 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 Twin Falls County?
Based on EPA SDWIS data, Twin Falls County has a water quality grade of C (52.8/100). 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).
Why does Twin Falls County have so many water violations?
Twin Falls County has 9 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 Twin Falls County rank for water quality in Idaho?
Twin Falls County ranks #9 out of 44 counties in Idaho by SDWIS water quality score (1 = best). With a score of 52.8/100, 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

Bannock County

Idaho

C

53.8

Water score

Gem County

Idaho

C

51.2

Water score

Ada County

Idaho

C

55.6

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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