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County water report

Seneca County Water Report

Drinking-water compliance, watershed health, monitoring records, and river conditions for Seneca County, Ohio.

Water grade

D

Water score

50.6

State rank

#57

of 88

Health violations

6

EPA SDWIS, 5-year lookback

Watershed impaired

0.0%

5 water bodies assessed

Monitoring sites

43

3,497 recent measurements

Live streamflow

49%

Sandusky River at Tiffin OH

Water at a glance

Key Water Indicators for Seneca County

EPA SDWIS

Safety Grade

D

Score: 50.6 / 100

EPA SDWIS

Active Violations

6

5-year health-based lookback

EPA ATTAINS

Watershed Health

0% impaired

5 bodies assessed

USGS NWIS

Streamflow Snapshot

49% of mean

Sandusky River at Tiffin OH

EPA WQP

Monitoring Sites

43

3,497 recent readings

Source: EPA SDWIS · Safe Drinking Water Information System

Drinking Water Compliance

Compliance grade

D

Based on EPA SDWIS compliance history.

Water score

Higher scores indicate cleaner recent compliance records.

50.6/100

Health violations

6

Health-based violations

Violations per 100K served

15.4

Population-normalized SDWIS rate

Editorial analysis

Understanding Seneca County’s Water

Drinking Water Quality Overview

EPA SDWIS

Seneca County's drinking water received a D grade, scoring 50.6 out of 100. Over the past five years, EPA SDWIS records 6 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). None of the assessed waterways are listed as impaired (0 of 5 water bodies) across Seneca County's watersheds. 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 2026-05-14T14:45:00.000-04:00) puts Sandusky River at 529.0 cfs — well below its long-term average at 49% 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. Seneca County has moderate coverage with 43 active monitoring sites with 3,497 recent measurements on record. Predominant monitoring categories include physical and inorganics, minor, metals. 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 Seneca County

Water Verdict

Seneca County receives a below-average water quality assessment with a grade of D and a score of 50.6 out of 100. Residents should review their utility's Consumer Confidence Report and may want to consider additional water filtration for drinking.

Violation Context

Seneca County has recorded 6 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 15.4 violations per 100,000 people served, this rate is high and signals significant water quality management issues.

Consumer Guidance

Seneca County's drinking-water compliance is below average with a Grade D, indicating repeated or unresolved violations in the recent record. Seneca County's drinking-water compliance score is 50.6 out of 100. The violation rate for Seneca County is 15.4 per 100,000 people served. Residents are encouraged to use an NSF 53 or NSF 58-certified filter for drinking and cooking water until the underlying violations are resolved. Running tap water for 30 seconds before use and avoiding older lead-pipe connections can also reduce exposure risk. The current Consumer Confidence Report from your utility will specify the contaminants of concern. With 43 active water-quality monitoring sites in Seneca County, data coverage is strong. A pipeline streamflow snapshot from the Sandusky River gauge is also available on this page.

Regional Context

Seneca County has poorer water quality than the average county in Ohio. Its water score is 5.6 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 Seneca County's water environment

Official EPA Resources for Seneca County

EPA How's My Waterway

Interactive watershed health data for Seneca County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Seneca County

Consumer Confidence Reports (OH)

Annual water quality reports from utilities in Ohio

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

0.0%

0 of 5 assessed

Mostly healthy

Top Impairment Causes

No specific impairment causes reported for the assessed water bodies in this county.

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

43

Active in the past 5 years

Measurements Recorded

3.5K

3,497 total readings

Most Measured

  • Physical
  • Inorganics, Minor, Metals
  • Nutrient

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

529cfs

May 14, 6:45 PM UTC

vs Long-Term Average

49%

Well below typical

Primary Streamgage

Sandusky River at Tiffin OH

USGS site
04197137
Drainage area
966 sq mi
Long-term mean
1,082 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 Seneca 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 Seneca County, Ohio?
Seneca County, Ohio has a drinking-water quality grade of D with a score of 50.6/100, based on EPA SDWIS compliance data. The county has 6 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 Seneca County?
Seneca County has 6 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 Seneca County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 0.0% of Seneca County's 5 assessed water bodies are classified as impaired (0 impaired). 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 Seneca County?
EPA's Water Quality Portal records 3,497 measurements from 43 monitoring sites in Seneca County over the past five years. The most frequently measured characteristic groups are Physical, Inorganics, Minor, Metals, Nutrient. 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 Seneca County right now?
Seneca County's primary USGS streamgage on the Sandusky River has a pipeline snapshot of 529 cubic feet per second — 49% of the long-term mean of 1,081.75 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 Seneca County water compare to the Ohio average?
Seneca County's SDWIS water quality score of 50.6/100 is lower than the Ohio state average of 56.2. The average water quality grade across Ohio is D, based on data from 88 counties with available SDWIS data.
Is tap water safe to drink in Seneca County?
Based on EPA SDWIS data, Seneca County has a water quality grade of D (50.6/100). 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 Seneca County have so many water violations?
Seneca County has 6 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 Seneca County rank for water quality in Ohio?
Seneca County ranks #57 out of 88 counties in Ohio by SDWIS water quality score (1 = best). With a score of 50.6/100, 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

Darke County

Ohio

D

50.4

Water score

Brown County

Ohio

C

51.0

Water score

Pickaway County

Ohio

D

49.7

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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