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Federal water data

County water report

Decatur County Water Report

Drinking-water compliance, watershed health, monitoring records, and river conditions for Decatur County, Iowa.

Water grade

F

Water score

11.1

State rank

#98

of 99

Health violations

16

EPA SDWIS, 5-year lookback

Watershed impaired

Not reported

EPA ATTAINS coverage varies by state

Monitoring sites

7

2,624 recent measurements

Live streamflow

30%

Thompson River at Davis City, IA

Water at a glance

Key Water Indicators for Decatur County

EPA SDWIS

Safety Grade

F

Score: 11.1 / 100

EPA SDWIS

Active Violations

16

5-year health-based lookback

EPA ATTAINS

Watershed Health

Not reported

Coverage varies by state

USGS NWIS

Streamflow Snapshot

30% of mean

Thompson River at Davis City, IA

EPA WQP

Monitoring Sites

7

2,624 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.

11.1/100

Health violations

16

Health-based violations

Violations per 100K served

291.7

Population-normalized SDWIS rate

Editorial analysis

Understanding Decatur County’s Water

Drinking Water Quality Overview

EPA SDWIS

Decatur County's water systems carry a failing grade, scoring 11.1 out of 100. Over the past five years, EPA SDWIS records 16 health-based violations — a pattern that public water utilities are required to disclose and correct.

River & Streamflow Status

USGS NWIS

USGS NWIS gauge data (as of 2026-05-14T13:00:00.000-05:00) puts Thompson River at 120.0 cfs — well below its long-term average at 30% of mean — low-flow conditions worth noting for water-dependent ecosystems. 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. Decatur County has limited coverage with 7 active monitoring sites with 2,624 recent measurements on record. Predominant monitoring categories include physical 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 Decatur County

Water Verdict

Decatur County receives a poor water quality assessment with a grade of F and a score of 11.1 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.

Violation Context

Decatur County has recorded 16 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 291.7 violations per 100,000 people served, this rate is high and signals significant water quality management issues.

Consumer Guidance

Drinking-water compliance in Decatur County is rated Grade F, reflecting significant health-based violations in the recent reporting period. Decatur County's drinking-water compliance score is 11.1 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. There are 7 active water-quality monitoring sites in Decatur County. A pipeline streamflow snapshot from the Thompson River gauge is also available on this page.

Regional Context

Decatur County has poorer water quality than the average county in Iowa. Its water score is 60.6 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 Decatur County's water environment

Official EPA Resources for Decatur County

EPA How's My Waterway

Interactive watershed health data for Decatur County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Decatur County

Consumer Confidence Reports (IA)

Annual water quality reports from utilities in Iowa

Past 5 years

Water Quality Monitoring

Monitoring Sites

7

Active in the past 5 years

Measurements Recorded

2.6K

2,624 total readings

Most Measured

  • Physical
  • 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

120cfs

May 14, 6:00 PM UTC

vs Long-Term Average

30%

Well below typical

Primary Streamgage

Thompson River at Davis City, IA

USGS site
06898000
Drainage area
701 sq mi
Long-term mean
404 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

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Water Cost Estimate

3

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Annual Total

$558

Monthly

$47

Water Bill

$558/yr

Filter Cost

$0/yr

Safety Grade for Decatur County:F — Failing

High violation count or severe watershed conditions.

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 Decatur County, Iowa?
Decatur County, Iowa has a drinking-water quality grade of F with a score of 11.1/100, based on EPA SDWIS compliance data. The county has 16 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 Decatur County?
Decatur County has 16 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 much water-quality monitoring happens in Decatur County?
EPA's Water Quality Portal records 2,624 measurements from 7 monitoring sites in Decatur County over the past five years. The most frequently measured characteristic groups are Physical, 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 Decatur County right now?
Decatur County's primary USGS streamgage on the Thompson River has a pipeline snapshot of 120 cubic feet per second — 30% of the long-term mean of 404.46 cfs. This is well below typical — often a signal of drought stress on source water. For the latest gauge feed, visit waterdata.usgs.gov.
How does Decatur County water compare to the Iowa average?
Decatur County's SDWIS water quality score of 11.1/100 is lower than the Iowa state average of 71.7. The average water quality grade across Iowa is C, based on data from 99 counties with available SDWIS data.
Is tap water safe to drink in Decatur County?
Based on EPA SDWIS data, Decatur County has a water quality grade of F (11.1/100). 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 Decatur County have so many water violations?
Decatur County has 16 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 Decatur County rank for water quality in Iowa?
Decatur County ranks #98 out of 99 counties in Iowa by SDWIS water quality score (1 = best). With a score of 11.1/100, it falls in the bottom 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

Calhoun County

Iowa

F

11.2

Water score

Iowa County

Iowa

F

11.3

Water score

Mills County

Iowa

F

10.8

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.

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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