Colusa Co. Service Area #2 - Stonyford
What EPA’s and California’s records show in this utility’s water: nitrate, arsenic and other regulated chemicals; lead and copper; and violations since 2016, with the certification that handles each result.
- Serves
- 160 people
- Connections
- 57
- Water source
- Groundwater
- Based in
- Colusa, CA
- County
- Colusa
- Owner
- Local government
- Hardness
- Hard
The ZIP code it serves
The short answer
Nothing in EPA’s and California’s records for this utility is above a health goal. That covers nitrate, arsenic and other regulated chemicals, plus lead and copper, not everything. No health-based violations on file since 2016.
What was found
Total trihalomethanes (TTHM), haloacetic acids (HAA5), nitrate, arsenic and uranium: California’s own results, samples taken from July 16, 2020 to Aug. 21, 2025, with EPA’s 2012 to 2019 file for earlier years.
Fluoride and chromium (total): EPA’s compliance monitoring file, samples taken from Aug. 9, 2012 to July 18, 2019. Newer results are in the utility’s annual water quality report.
Below EPA’s limits5
Total trihalomethanes (TTHM)
Forms or is added in treatment
35ppb
Highest yearly average, 2020 to 2025
Averaged by year, the highest was 35 ppb, in 2025, below EPA’s legal limit of 80 ppb. That was also the latest year on file. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 24 ppb, in 2017.
What handles it
- NSF/ANSI 53 look for “Trihalomethanes (TTHM) Reduction”
- NSF/ANSI 58 look for “Trihalomethanes (TTHM) Reduction”
Haloacetic acids (HAA5)
Forms or is added in treatment
8.0ppb
Highest yearly average, 2020 to 2025
2025: not found
Averaged by year, the highest was 8.0 ppb, in 2020, below EPA’s legal limit of 60 ppb. In 2025, the latest year on file, it wasn’t found in its one sample. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 4.0 ppb, in 2017.
What handles it
No certification claim covers this compound yet.
Nitrate
Comes from the source
0.6ppm
Highest sample; found in 1 of 6
2025: not found
The highest sample, in 2020, was 0.6 ppm, below EPA’s legal limit of 10 ppm. In 2025, the latest year on file, it wasn’t found in its one sample. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 3.7 ppm, in 2019.
What handles it
- NSF/ANSI 58 look for “Nitrate/Nitrite Reduction”
- NSF/ANSI 53 look for “Nitrate/Nitrite (30 ppm challenge)”
Fluoride
Forms or is added in treatment
0.1ppm
Highest yearly average, 2012 to 2019
2019: not found
Averaged by year, the highest was 0.1 ppm, in 2015, below EPA’s legal limit of 4.0 ppm. In 2019, the latest year on file, it wasn’t found in its one sample.
What handles it
- NSF/ANSI 58 look for “Fluoride Reduction”
- NSF/ANSI 53 look for “Fluoride”
Chromium (total)
Comes from the source
1.5ppb
Highest yearly average, 2013 to 2019
2019: not found
Averaged by year, the highest was 1.5 ppb, in 2013, below EPA’s legal limit of 100 ppb. Its highest single sample was 2.0 ppb. In 2019, the latest year on file, it wasn’t found in any of its two samples.
What handles it
- NSF/ANSI 58 look for “Chromium (Hexavalent) Reduction”
- NSF/ANSI 53 look for “Chromium Reduction”
3 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
- Arsenic
- Lead
- Uranium
Hardness
Hard, 138 mg/L (8.1 grains per gallon), at its one sampling point, in 2019.
Hardness is calcium and magnesium. EPA sets no limit for it: it shows up as scale on fixtures and in water heaters, and as soap that won’t lather. USGS calls water above 60 mg/L moderately hard, above 120 hard and above 180 very hard.
Violations since 2016
No health-based violations on file with EPA since 2016. There are 3 monitoring or reporting violations: a sample missed, late or not reported.
What this report can’t tell you
Everything else. Total trihalomethanes (TTHM), haloacetic acids (HAA5), nitrate, arsenic and uranium results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Fluoride and chromium (total) come from EPA’s file alone, which ends in 2019. Colusa Co. Service Area #2 - Stonyford’s own annual report, which it must send you every year, has newer results for those and the contaminants this page does not show.
Your own plumbing. Lead results are the 90th percentile across homes the utility samples. Your home’s service line, solder and fixtures decide yours. A certified lab test is the only way to know.
What it means for your health. This page reports what the records show and EPA’s limits and goals; it is not medical advice. If you are worried about a health effect, talk to a doctor or your local health department.
Anything after the latest data. SDWIS data is from 2026 Q3; UCMR 5 didn’t sample this utility; California’s results run from July 16, 2020 to Aug. 21, 2025; EPA’s compliance samples are from Aug. 9, 2012 to July 18, 2019.
Testing your own tap
The 3 labs California certifies closest to the area Colusa Co. Service Area #2 - Stonyford serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.
Alpha Analytical Laboratories, Inc. - Ukiah
Ukiah, CA · about 39 miles
Certified for bacteria, nitrate, lead and copper, metals, minerals and other inorganics, organic chemicals, disinfection byproducts, radioactivity
Fruit Growers Laboratory, Inc.
Chico, CA · about 47 miles
Certified for bacteria
K Prime, LLC.
Santa Rosa, CA · about 57 miles
Certified for bacteria, nitrate, lead and copper, metals, minerals and other inorganics, PFAS
Sources
- EPA UCMR 5 occurrence data, file of Oct. 15, 2026
- EPA SDWA bulk download (SDWIS federal data), 2026 Q3
- California State Water Resources Control Board, Division of Drinking Water, results from Jan. 1, 2020 to July 17, 2026, read Oct. 8, 2026
- EPA Six-Year Review 4 compliance monitoring data, 2012 to 2019, file of Feb. 5, 2024
- Certified labs: California State Water Resources Control Board, ELAP accredited laboratories and their fields of accreditation, read Oct. 17, 2026; distances from the Census 2020 ZIP code tabulation area gazetteer
- Hardness: California State Water Resources Control Board, Division of Drinking Water, results from July 18, 2019 to July 18, 2019, read Oct. 10, 2026
- Limits and goals: each contaminant’s page, with its EPA source.
- How this page is built: methodology.
PWSID CA0600005. Rebuilt from EPA data on Oct. 18, 2026.
What to do next
- Nothing here is above a health goalIn EPA’s and California’s records for this utility. They don’t cover everything, which is why the next step matters.Every contaminant TapBuff tracks
- Get the utility’s own reportColusa Co. Service Area #2 - Stonyford must send you a water quality report every year. It covers contaminants this page does not show, and has newer results than EPA’s national file for the ones here that come from it.How to read it
- Test your own tap for leadYour service line, solder and fixtures decide the lead at your faucet, not the utility’s average.Lead in your water: what to do
- Decide if you want a filter at allA filter for taste or chlorine is a preference, not a need. The standards say what each kind can do.NSF/ANSI standards, decoded