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EPA SDWIS

Modoc County Water Quality

Modoc County, California

Water Grade

F

Water Score

31.1

Violations

3

State Rank

#42

of 58 (1 = best)

EPA SDWIS Compliance

Drinking Water Quality

Water Quality Grade

F

Based on EPA compliance history and violation data

Water Score

31.1/100

Higher = better quality

Health Violations

3

Health-based violations

Violation Rate

61.0%

Systems with violations

Water Advisory: Modoc County

Water Verdict

Modoc County receives a poor water quality assessment with a grade of F and a score of 31.1 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

Modoc County has recorded 3 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 61.0 violations per 1,000 residents, this rate is high and signals significant water quality management issues.

Consumer Guidance

Residents of Modoc 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 3 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

Modoc County has poorer water quality than the average county in California. Its water score is 13.5 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

22.1%

15 of 68 assessed

Some impairment

Top Impairment Causes

  • 1

    PH

  • 2

    TOTAL DISSOLVED SOLIDS (TDS)

  • 3

    DISSOLVED OXYGEN

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

16

Active in the past 5 years

Measurements Recorded

1.0K

1,017 total readings

Most Measured

  • Organics, Pesticide
  • Organics, Other
  • 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

1.08cfs

May 14, 6:45 PM UTC

vs Long-Term Average

1%

Well below typical

Primary Streamgage

PIT R NR CANBY CA

USGS site
11348500
Drainage area
1,431 sq mi
Long-term mean
230 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 Modoc County, California?
Modoc County, California has a drinking-water quality grade of F with a score of 31.1/100, based on EPA SDWIS compliance data. The county has 3 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 Modoc County?
Modoc County has 3 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 Modoc County?
EPA ATTAINS assessments under Clean Water Act §303(d) indicate 22.1% of Modoc County's 68 assessed water bodies are classified as impaired (15 impaired). The top reported causes are PH, TOTAL DISSOLVED SOLIDS (TDS), DISSOLVED OXYGEN. 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 Modoc County?
EPA's Water Quality Portal records 1,017 measurements from 16 monitoring sites in Modoc County over the past five years. The most frequently measured characteristic groups are Organics, Pesticide, Organics, Other, 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 Modoc County right now?
Modoc County's primary USGS streamgage on the PIT R is currently reading 1.08 cubic feet per second — 1% of the long-term mean of 230.11 cfs. This is well below typical — often a signal of drought stress on source water. For genuine real-time data, visit waterdata.usgs.gov.
How does Modoc County water compare to the California average?
Modoc County's SDWIS water quality score of 31.1/100 is lower than the California state average of 44.6. The average water quality grade across California is D, based on data from 58 counties with available SDWIS data.
Is tap water safe to drink in Modoc County?
Based on EPA SDWIS data, Modoc County has a water quality grade of F (31.1/100). 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).
Does Modoc County have clean drinking water?
Modoc County has 3 health-based drinking water violations according to EPA records. With a water quality score of 31.1/100 and grade F, the county's drinking water has had some compliance issues but continues to be monitored. Note: drinking-water compliance speaks to the public water system, not necessarily to the watershed itself — check the Watershed Health zone for ATTAINS §303(d) data.
How does Modoc County rank for water quality in California?
Modoc County ranks #42 out of 58 counties in California by SDWIS water quality score (1 = best). With a score of 31.1/100, 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

Kern County

California

F

30.0

Water score

Napa County

California

F

33.4

Water score

Tuolumne County

California

F

34.0

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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