waterbycounty
Compiled federal source snapshot

Idaho Water Quality

Drinking water data for all 44 counties.

Avg SDWIS Compliance Index

29.9

Most Common Five-Year SDWIS Compliance Band

F

Counties with Data

44

of 44 total

County water atlas

Idaho water signals by county

A state-level 2.5D view across drinking-water compliance, watershed impairment, monitoring density, and streamflow snapshot context. Pin any county, switch layers, then use the lens controls to compare index ranges, recorded violation rates, or impaired watersheds without leaving the page.

Counties

44

Avg SDWIS index

29.9

Watersheds

44

ATTAINS counties

Monitoring

44

35 fresh USGS snapshots

State atlas layers combine EPA SDWIS health-based violations, EPA ATTAINS 303(d) impairment assessments, EPA Water Quality Portal monitoring sites, and representative USGS NWIS streamflow gauges. Streamflow values appear only for fresh pipeline snapshots, not as a continuously updated stream. County pages include the observation time and year.

Prepared by ByCounty Editorial TeamPublished by WaterByCounty

Multi-source coverage in Idaho

Beyond Drinking Water

EPA SDWIS

44/ 44

counties with drinking-water compliance data

553 health violations statewide (5yr)

EPA ATTAINS

63.3%

avg impaired across 44 counties

5,988 of 10,235 assessed bodies impaired

EPA WQP

2,222

monitoring sites across 44 counties

409,673 total readings (5yr window)

USGS NWIS

35

counties with a fresh pipeline snapshot

5 above27 below

State atlas notes

What stands out in Idaho

County water quality is not one number. The strongest read comes from comparing drinking-water compliance against watershed impairment, monitoring density, and streamflow context. Use these signals as a starting point, then open any county profile for source-level detail.

Compliance spread

Custer County has the highest value in the published state SDWIS Compliance Index table at 86.2/100, while Fremont County has the lowest at 1.9/100. That is a 84.3 point gap inside one state.

Zero health violations

4

3+ health violations

27

Watershed pressure

The atlas impairment layer points to counties where assessed water bodies are most likely to miss state quality standards. Assessment density varies, so compare the percentage with the number of assessed bodies on the county page.

Minidoka County83.3%Canyon County82.9%Jefferson County81.9%

Monitoring hubs

Butte County195 sitesIdaho County176 sitesMinidoka County171 sites

Lowest flow reads

Butte County0%Blaine County0%Camas County1%

Highest fresh streamflow pipeline snapshots: Jefferson County (206%, observation 2026), Bear Lake County (183%, observation 2026), Power County (151%, observation 2026). These are source-data observations, not household tap-water conclusions.

All Idaho Counties

CountySDWIS Compliance Index
Custer County86.2
Oneida County86.2
Shoshone County86.2
Washington County86.2
Ada County60.1
Nez Perce County57.3
Twin Falls County56.7
Bannock County48.8
Jerome County45.1
Gem County44.0
Canyon County40.2
Bear Lake County39.9
Minidoka County39.7
Caribou County37.7
Jefferson County37.2
Bonneville County36.9
Kootenai County36.7
Payette County32.6
Teton County32.3
Latah County30.6
Gooding County28.1
Lincoln County27.4
Madison County21.6
Bingham County20.2
Benewah County19.8
Owyhee County17.9
Butte County17.8
Adams County15.4
Bonner County12.1
Cassia County12.0
Idaho County11.8
Clearwater County11.6
Blaine County10.6
Power County10.6
Elmore County9.9
Clark County7.8
Camas County6.8
Lemhi County6.8
Boise County5.8
Lewis County5.5
Franklin County5.3
Boundary County3.4
Valley County3.3
Fremont County1.9

Frequently Asked Questions

Which Idaho county has the highest SDWIS Compliance Index?
Custer County has the highest SDWIS Compliance Index in the published Idaho cohort at 86.2/100. This WaterByCounty relative comparison is not an EPA score and does not establish current conditions for a utility or address.
What does the Five-Year SDWIS Compliance Band mean?
The band is derived only from each county aggregation's recorded health-violation rate per 100,000 people served for the stated five-year source window. It is separate from the relative SDWIS Compliance Index and is not a current determination for a specific utility or address.
What does EPA ATTAINS report across Idaho?
Across 44 published Idaho county records with EPA ATTAINS data, 5,988 of 10,235 assessed water bodies are listed as impaired. This is a watershed assessment and does not describe finished household tap water.
Which USGS streamflow records are shown across Idaho?
WaterByCounty has 35 fresh USGS pipeline snapshots in the published Idaho cohort. Each county page shows its observation timestamp and year. A pipeline snapshot is not a continuously updated reading or a tap-water safety measure.
Where can Idaho residents find current official information?
Review the applicable utility's Consumer Confidence Report, active notices, and the state drinking-water agency. WaterByCounty's county-level historical aggregations do not establish the current status of a specific utility, address, private well, or household plumbing system.
What does Water Quality Portal monitoring volume show in Idaho?
The published county records contain 409,673 results from 2,222 monitoring locations in the site's five-year aggregation. Monitoring volume does not by itself indicate better or worse water quality.

Data Sources

Drinking-water compliance data from the EPA Safe Drinking Water Information System (SDWIS) via the ECHO enforcement database. The WaterByCounty SDWIS Compliance Index reflects the recorded rate and is not an EPA score.

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.

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