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EPA SDWIS

LaSalle County Water Quality

LaSalle County, Illinois

Water Grade

F

Water Score

15.3

Violations

182

State Rank

#98

of 102 (1 = best)

EPA SDWIS Compliance

Drinking Water Quality

Water Quality Grade

F

Based on EPA compliance history and violation data

Water Score

15.3/100

Higher = better quality

Health Violations

182

Health-based violations

Violation Rate

193.2%

Systems with violations

Water Advisory: LaSalle County

Water Verdict

LaSalle County receives a poor water quality assessment with a grade of F and a score of 15.3 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

LaSalle County has recorded 182 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 193.2 violations per 1,000 residents, this rate is high and signals significant water quality management issues.

Consumer Guidance

Residents of LaSalle County are advised to use filtered or bottled water for drinking and cooking until water quality improves. A reverse-osmosis or activated-carbon filter certified to remove the contaminants listed in the utility's Consumer Confidence Report is recommended. With 182 recorded health violations, staying informed about utility communications and boil-water notices is especially important. For long-term peace of mind, request your utility's latest Consumer Confidence Report and consider independent water testing if you have specific health concerns.

Regional Context

LaSalle County has poorer water quality than the average county in Illinois. Its water score is 32.5 points lower than the state average, suggesting more challenges with contamination control or infrastructure than neighboring counties.

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

42.7%

291 of 681 assessed

Moderate concern

Top Impairment Causes

  • 1

    PHOSPHORUS, TOTAL

  • 2

    MERCURY

  • 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

31

Active in the past 5 years

Measurements Recorded

12K

11,610 total readings

Most Measured

  • Physical
  • Inorganics, Minor, Metals
  • Organics, Other

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

7,860cfs

May 14, 6:45 PM UTC

vs Long-Term Average

73%

Below typical

Primary Streamgage

ILLINOIS RIVER AT MARSEILLES, IL

USGS site
05543500
Drainage area
8,259 sq mi
Long-term mean
10.8K 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; "% of typical" compares the latest reading against that average.

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Frequently Asked Questions

What is the water quality in LaSalle County, Illinois?
LaSalle County, Illinois has a drinking-water quality grade of F with a score of 15.3/100, based on EPA SDWIS compliance data. The county has 182 health-based drinking water violations over the past 5 years. Watershed health, monitoring records, and live streamflow are reported separately on this page.
Are there any water violations in LaSalle County?
LaSalle County has 182 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 LaSalle County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 42.7% of LaSalle County's 681 assessed water bodies are classified as impaired (291 impaired). The top reported causes are PHOSPHORUS, TOTAL, MERCURY, 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 LaSalle County?
EPA's Water Quality Portal records 11,610 measurements from 31 monitoring sites in LaSalle County over the past five years. The most frequently measured characteristic groups are Physical, Inorganics, Minor, Metals, Organics, Other. 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 LaSalle County right now?
LaSalle County's primary USGS streamgage on the ILLINOIS RIVER is currently reading 7,860 cubic feet per second — 73% of the long-term mean of 10,826.45 cfs. Flow is within typical range for this gauge. For genuine real-time data, visit waterdata.usgs.gov.
How does LaSalle County water compare to the Illinois average?
LaSalle County's SDWIS water quality score of 15.3/100 is lower than the Illinois state average of 47.8. The average water quality grade across Illinois is D, based on data from 102 counties with available SDWIS data.
Is tap water safe to drink in LaSalle County?
Based on EPA SDWIS data, LaSalle County has a water quality grade of F (15.3/100). 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 LaSalle County have so many water violations?
LaSalle County has 182 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 LaSalle County rank for water quality in Illinois?
LaSalle County ranks #98 out of 102 counties in Illinois by SDWIS water quality score (1 = best). With a score of 15.3/100, 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

Wayne County

Illinois

F

15.4

Water score

Johnson County

Illinois

F

15.8

Water score

Macoupin County

Illinois

F

16.5

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, 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 Logan Johnson, Founder & Data EditorUpdated Reviewed by Logan Johnson, Founder & Data Editor

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