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Compiled federal source snapshot

County water report

Sonoma County Water Report

Drinking-water compliance, watershed health, monitoring records, and river conditions for Sonoma County, California.

Five-Year SDWIS Compliance Band

C

SDWIS Compliance Index

46.4

State rank

#29

of 58

Health violations

54

EPA SDWIS, 5-year lookback

Watershed impaired

77.8%

36 water bodies assessed

Monitoring sites

52

17,446 recent measurements

USGS streamflow snapshot

5%

Observation year 2026

Water at a glance

Key Water Indicators for Sonoma County

EPA SDWIS

Five-Year SDWIS Compliance Band

C

SDWIS Compliance Index: 46.4 / 100

EPA SDWIS

Recorded Health Violations

54

Stated five-year SDWIS source window

EPA ATTAINS

Watershed Health

78% impaired

36 bodies assessed

USGS NWIS

Streamflow Snapshot

5% of mean

Observation year 2026

EPA WQP

Monitoring Sites

52

17,446 recent readings

Source: EPA SDWIS · Safe Drinking Water Information System

Drinking Water Compliance

Five-Year SDWIS Compliance Band

C

Derived from the recorded five-year SDWIS violation rate.

SDWIS Compliance Index

WaterByCounty relative national comparison; not an EPA score.

46.4/100

Recorded health violations

54

Health-based violations

Violations per 100K served

12.2

Population-normalized SDWIS rate

Source-specific observations

Recorded Water Data for Sonoma County

Recorded SDWIS Compliance Data

EPA SDWIS

In WaterByCounty's county-level SDWIS aggregation, 54 records are categorized as health-based violations during the stated five-year source window. This does not establish the current status of any specific utility or address. Review your utility's current Consumer Confidence Report and active notices for current information.

Watershed Conditions

EPA ATTAINS

EPA ATTAINS lists 28 of 36 assessed water bodies associated with this county as impaired in reporting cycle 2022. This is a watershed assessment and does not describe finished household tap water.

USGS Streamflow Snapshot

USGS NWIS

The selected USGS gauge recorded 112 cfs at 2026-08-06T08:15:00.000-07:00 (observation year 2026), equal to 5.2% of the full-record annual mean used by this site. This is a pipeline snapshot, not a continuously updated reading or a tap-water safety measure.

Monitoring Network

EPA WQP

The Water Quality Portal contains 17,446 results from 52 monitoring locations in the site's five-year aggregation. Monitoring volume does not by itself indicate better or worse water quality.

Source facts

EPA SDWIS county aggregation

Recorded compliance data

In WaterByCounty's county-level SDWIS aggregation, 54 records are categorized as health-based violations during the stated five-year source window.

Coverage limitation

This does not establish the current status of any specific utility or address.

Current official source

Review your utility's current Consumer Confidence Report and active notices for current information.

County-level historical records do not establish current conditions for a specific utility, address, private well, or household plumbing system.

Contaminants & Resources

Recorded watershed and public-system source links for Sonoma County

Watershed Impairment Causes (EPA ATTAINS)

  • 1

    Sedimentation and siltation

    Impairment cause per EPA Clean Water Act §303(d) assessment

  • 2

    Elevated temperature

    Impairment cause per EPA Clean Water Act §303(d) assessment

  • 3

    Pathogens

    Impairment cause per EPA Clean Water Act §303(d) assessment

Source: EPA ATTAINS · Reporting cycle 2022

This is a watershed assessment and does not describe finished household tap water.

Official EPA Resources for Sonoma County

EPA How's My Waterway

Interactive watershed health data for Sonoma County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Sonoma County

Consumer Confidence Reports (CA)

Annual water quality reports from utilities in California

Clean Water Act §303(d)

Watershed Health

Impaired Water Bodies

77.8%

28 of 36 assessed

60%+ impaired

Top Impairment Causes

  • 1

    SEDIMENTATION/SILTATION

  • 2

    TEMPERATURE

  • 3

    PATHOGENS

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). This is a watershed assessment and does not describe finished household tap water. Assessment coverage varies by state; counties without assessed water bodies are not shown.

Past 5 years

Water Quality Monitoring

Monitoring Sites

52

Included in the site's five-year aggregation

Measurements Recorded

17K

17,446 total readings

Most Measured

  • Physical
  • Inorganics, Minor, Metals
  • Microbiological

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). Monitoring volume does not by itself indicate better or worse water quality.

USGS streamflow snapshot

River & Stream Conditions

Pipeline Snapshot

112cfs

Aug 6, 2026, 3:15 PM UTC

vs Long-Term Average

5%

Well below typical

Primary Streamgage

RUSSIAN R A HACIENDA BRIDGE NR GUERNEVILLE CA

USGS site
11467000
Drainage area
1,338 sq mi
Long-term mean
2,163 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 comparison appears only when the compiled observation is fresh. A pipeline snapshot is not a continuously updated reading or a tap-water safety measure.

Free tool

Estimate Your Water Costs

This cost-only tool appears here for convenience. It uses editable national starting assumptions and user-entered inputs—not Sonoma County water records or a reported local utility rate.

Household Water Cost Estimate

Start with editable national budgeting assumptions, then replace them with your own usage and bill rates. Every result uses the user-entered values below; none is a reported local utility rate.

Annual use

109,500 gal

Annual water

$744.60

Annual wastewater

$350.40

Annual total

$1,095.00

Monthly total

$91.25

Starting values are an editable national budgeting example: four people, 300 gallons per day, $6.80 per 1,000 gallons for water, and $3.20 per 1,000 gallons for wastewater. Bills can also include fixed fees, tiers, taxes, minimum charges, and billing periods that this estimate does not model.

Open the full calculator →

Frequently Asked Questions

What did the SDWIS aggregation record for Sonoma County?
In WaterByCounty's county-level SDWIS aggregation, 54 records are categorized as health-based violations during the stated five-year source window. This does not establish the current status of any specific utility or address. Review your utility's current Consumer Confidence Report and active notices for current information.
How are the SDWIS Compliance Index and Five-Year SDWIS Compliance Band defined?
The SDWIS Compliance Index is WaterByCounty's relative 0–100 comparison derived from the recorded health-violation rate. The Five-Year SDWIS Compliance Band is an absolute A–F category derived from that rate for 2021-07-31 through 2026-07-31. Neither is an EPA score or a current determination for a specific utility or address.
What does EPA ATTAINS report for Sonoma County?
EPA ATTAINS lists 28 of 36 assessed water bodies associated with this county as impaired in reporting cycle 2022. This is a watershed assessment and does not describe finished household tap water.
How much Water Quality Portal monitoring is recorded for Sonoma County?
The Water Quality Portal contains 17,446 results from 52 monitoring locations in the site's five-year aggregation. Monitoring volume does not by itself indicate better or worse water quality.
What USGS streamflow information is shown for Sonoma County?
The selected USGS gauge recorded 112 cfs at 2026-08-06T08:15:00.000-07:00 (observation year 2026), equal to 5.2% of the full-record annual mean used by this site. This is a pipeline snapshot, not a continuously updated reading or a tap-water safety measure.
Where can I find current official information for Sonoma County?
Review the applicable utility's Consumer Confidence Report, active notices, and the state drinking-water agency. County-level historical aggregations do not establish the current status of a specific utility, address, private well, or household plumbing system.

Counties with Similar SDWIS Compliance Index Values

Contra Costa County

California

C

47.1

SDWIS Compliance Index

Napa County

California

C

45.2

SDWIS Compliance Index

Imperial County

California

C

47.6

SDWIS Compliance Index

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.

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.

Streamflow pipeline snapshots from the USGS National Water Information System (NWIS), using the selected largest-drainage gauge in each county and its full-record annual mean. Snapshot and comparison copy appears only for observations marked fresh by the pipeline.

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.

Prepared by ByCounty Editorial TeamPublished by WaterByCountyPublished

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