Riverside CSD
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
- 333 people
- Connections
- 101
- Water source
- Groundwater
- Based in
- Ferndale, CA
- County
- Humboldt
- 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), nitrate, fluoride, haloacetic acids (HAA5), arsenic and chromium (total): California’s own results, samples taken from Aug. 25, 2020 to Aug. 26, 2025, with EPA’s 2012 to 2019 file for earlier years.
Below EPA’s limits4
Total trihalomethanes (TTHM)
Forms or is added in treatment
12ppb
Highest yearly average, 2020 to 2024
2024, one sample: 8.7 ppb
Averaged by year, the highest was 12 ppb, in 2020, below EPA’s legal limit of 80 ppb. Its highest single sample was 13.4 ppb. In 2024, the latest year on file, its one sample was 8.7 ppb.
What handles it
- NSF/ANSI 53 look for “Trihalomethanes (TTHM) Reduction”
- NSF/ANSI 58 look for “Trihalomethanes (TTHM) Reduction”
Nitrate
Comes from the source
1.2ppm
Highest sample; found in 12 of 12
2025 average: 0.86 ppm
The highest sample, in 2020, was 1.2 ppm, below EPA’s legal limit of 10 ppm. In 2025, the latest year on file, its two samples averaged 0.86 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 1.1 ppm, in 2012.
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
0.4ppm
Highest yearly average, 2024
Averaged by year, the highest was 0.4 ppm, in 2024, below EPA’s legal limit of 4.0 ppm. That is the only year on file. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.35 ppm, in 2015.
What handles it
- NSF/ANSI 58 look for “Fluoride Reduction”
- NSF/ANSI 53 look for “Fluoride”
Haloacetic acids (HAA5)
Forms or is added in treatment
2.6ppb
Highest yearly average, 2020 to 2024
2024: not found
Averaged by year, the highest was 2.6 ppb, in 2020, below EPA’s legal limit of 60 ppb. In 2024, the latest year on file, it wasn’t found in its one sample.
What handles it
No certification claim covers this compound yet.
3 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
- Arsenic
- Chromium (total)
- Lead
Hardness
Hard, typically 140 mg/L (8.2 grains per gallon), across 2 sampling points, in 2024.
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 2 monitoring or reporting violations: a sample missed, late or not reported.
What this report can’t tell you
Everything else. Total trihalomethanes (TTHM), nitrate, fluoride, haloacetic acids (HAA5), arsenic and chromium (total) results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Riverside CSD’s own annual report, which it must send you every year, has 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 Aug. 25, 2020 to Aug. 26, 2025.
Testing your own tap
The 2 labs California certifies closest to the area Riverside CSD serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.
Humboldt County Public Health Laboratory
Eureka, CA · about 21 miles
Certified for bacteria
Microbac Laboratories, Inc. - Arcata
Arcata, CA · about 30 miles
Certified for bacteria, nitrate, lead and copper, metals, minerals and other inorganics, organic chemicals, disinfection byproducts
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 May 14, 2024 to July 23, 2024, read Oct. 10, 2026
- Limits and goals: each contaminant’s page, with its EPA source.
- How this page is built: methodology.
PWSID CA1200518. 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 reportRiverside CSD must send you a water quality report every year. It covers contaminants this page does not show.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