waterbycounty
Compiled federal source snapshot

Missouri Water Quality

Drinking water data for all 110 counties.

Avg SDWIS Compliance Index

50.4

Most Common Five-Year SDWIS Compliance Band

F

Counties with Data

110

of 110 total

County water atlas

Missouri 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

110

Avg SDWIS index

50.4

Watersheds

0

ATTAINS counties

Monitoring

110

83 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 Missouri

Beyond Drinking Water

EPA SDWIS

110/ 110

counties with drinking-water compliance data

392 health violations statewide (5yr)

EPA ATTAINS

—

No §303(d) assessments yet for Missouri

EPA WQP

1,805

monitoring sites across 110 counties

382,909 total readings (5yr window)

USGS NWIS

83

counties with a fresh pipeline snapshot

14 above68 below

State atlas notes

What stands out in Missouri

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

Atchison County has the highest value in the published state SDWIS Compliance Index table at 86.2/100, while Mercer County has the lowest at 3.5/100. That is a 82.7 point gap inside one state.

Zero health violations

32

3+ health violations

48

Monitoring hubs

Jackson County143 sitesSt. Louis County92 sitesFranklin County78 sites

Lowest flow reads

Barton County0%Vernon County1%Caldwell County4%

Highest fresh streamflow pipeline snapshots: Callaway County (4277%, observation 2026), Boone County (4107%, observation 2026), Johnson County (702%, observation 2026). These are source-data observations, not household tap-water conclusions.

All Missouri Counties

CountySDWIS Compliance Index
Atchison County86.2
Barton County86.2
Bollinger County86.2
Boone County86.2
Buchanan County86.2
Callaway County86.2
Carter County86.2
Christian County86.2
Clark County86.2
Cole County86.2
Cooper County86.2
Crawford County86.2
Dallas County86.2
Dent County86.2
Douglas County86.2
Grundy County86.2
Jackson County86.2
Johnson County86.2
Knox County86.2
Laclede County86.2
Macon County86.2
Madison County86.2
Maries County86.2
Polk County86.2
Putnam County86.2
Randolph County86.2
Shannon County86.2
St. Charles County86.2
St. Louis city86.2
St. Louis County86.2
Worth County86.2
Wright County86.2
Greene County68.5
Cape Girardeau County67.8
Jasper County67.4
Pulaski County62.9
Platte County61.1
Marion County60.7
Howell County59.8
Barry County59.6
Warren County57.3
Livingston County56.5
Jefferson County55.9
Clay County54.0
Perry County53.3
Adair County52.6
Butler County51.6
Camden County51.6
Cass County50.8
Audrain County50.3
Vernon County50.2
Phelps County48.7
Taney County48.7
Newton County48.5
Moniteau County48.4
Osage County45.8
Franklin County45.2
Linn County44.8
Lewis County44.3
Clinton County42.9
Dunklin County42.0
Webster County41.8
Andrew County41.5
Stoddard County40.8
Washington County39.9
Oregon County36.5
Ripley County35.7
Howard County35.5
Lafayette County35.4
Daviess County35.3
Stone County33.4
Lawrence County33.1
Sullivan County33.1
Saline County32.8
Montgomery County32.6
Wayne County32.3
Ralls County31.0
Dade County29.8
McDonald County29.5
Henry County29.3
Nodaway County29.2
St. Clair County28.6
Cedar County27.3
Texas County27.3
Gasconade County26.7
New Madrid County26.1
Pettis County25.9
Scott County24.9
Miller County24.7
Ste. Genevieve County24.0
Benton County23.5
Lincoln County23.3
Holt County22.9
Mississippi County22.0
St. Francois County20.1
Pike County19.7
Bates County18.1
Reynolds County17.7
Shelby County16.9
Harrison County16.8
Caldwell County16.2
Hickory County16.1
Chariton County14.0
Scotland County13.7
Morgan County12.0
DeKalb County10.1
Ozark County10.0
Iron County6.1
Monroe County4.9
Mercer County3.5

Frequently Asked Questions

Which Missouri county has the highest SDWIS Compliance Index?
Atchison County has the highest SDWIS Compliance Index in the published Missouri 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.
Which USGS streamflow records are shown across Missouri?
WaterByCounty has 83 fresh USGS pipeline snapshots in the published Missouri 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 Missouri 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 Missouri?
The published county records contain 382,909 results from 1,805 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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