Gran Mutual Water Co
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
- 290 people
- Connections
- 91
- Water source
- Groundwater
- Based in
- Chico, CA
- County
- Butte
- Owner
- Private
- Hardness
- Moderately 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
Nitrate, arsenic, fluoride, haloacetic acids (HAA5) and total trihalomethanes (TTHM): California’s own results, samples taken from Jan. 28, 2020 to Dec. 8, 2025, with EPA’s 2012 to 2019 file for earlier years.
Chromium (total): EPA’s compliance monitoring file, samples taken from March 12, 2018 to Jan. 11, 2019. Newer results are in the utility’s annual water quality report.
Below EPA’s limits1
Nitrate
Comes from the source
0.46ppm
Highest sample; found in 8 of 14
2025 average: 0.2 ppm
The highest sample, in 2024, was 0.46 ppm, below EPA’s legal limit of 10 ppm. In 2025, the latest year on file, its two samples averaged 0.2 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 1.3 ppm, in 2018.
What handles it
- NSF/ANSI 58 look for “Nitrate/Nitrite Reduction”
- NSF/ANSI 53 look for “Nitrate/Nitrite (30 ppm challenge)”
6 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
- Arsenic
- Chromium (total)
- Fluoride
- Haloacetic acids (HAA5)
- Lead
- Total trihalomethanes (TTHM)
Hardness
Moderately hard, typically 109 mg/L (6.4 grains per gallon), across 2 sampling points, 2019 to 2025.
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 is 1 monitoring or reporting violation: a sample missed, late or not reported.
What this report can’t tell you
Everything else. Nitrate, arsenic, fluoride, haloacetic acids (HAA5) and total trihalomethanes (TTHM) results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Chromium (total) comes from EPA’s file alone, which ends in 2019. Gran Mutual Water Co’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 Jan. 28, 2020 to Dec. 8, 2025; EPA’s compliance samples are from March 12, 2018 to Jan. 11, 2019.
Testing your own tap
The 3 labs California certifies closest to the area Gran Mutual Water Co serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.
Fruit Growers Laboratory, Inc.
Chico, CA · about 4 miles
Certified for bacteria
Cranmer Engineering, Inc.
Grass Valley, CA · about 53 miles
Certified for bacteria, nitrate, lead and copper, metals, minerals and other inorganics
Pace Analytical Services, LLC - Redding
Redding, CA · about 68 miles
Certified for bacteria
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 10, 2019 to Dec. 8, 2025, read Oct. 10, 2026
- Limits and goals: each contaminant’s page, with its EPA source.
- How this page is built: methodology.
PWSID CA0400008. 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 reportGran Mutual Water Co 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