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Del Norte 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
215 people
Connections
85
Water source
Groundwater
Based in
Somis, CA
County
Ventura
Owner
Private
Hardness
Very hard
The 2 ZIP codes it serves

93012, 93060

The short answer

3 results are above the health goal. The worst: Nitrate, above the health goal. 4 health-based violations since 2016.

What handles it

What was found

Nitrate, arsenic, uranium, fluoride, chromium (total), haloacetic acids (HAA5) and total trihalomethanes (TTHM): California’s own results, samples taken from Jan. 31, 2020 to May 13, 2026, with EPA’s 2012 to 2019 file for earlier years.

Above the health goal3

Nitrate

Comes from the source

Above the health goal

10.5ppm

Highest sample; found in 29 of 35

2026 average: 8.2 ppm

One sample, in 2023, was above EPA’s legal limit of 10 ppm, at 10.5 ppm. The next sample at the same point, within 30 days, brought the average back under the limit. 10 ppm is also EPA’s health goal. In 2026, the latest year on file, its three samples averaged 8.2 ppm. EPA recorded no violation for nitrate at this utility since 2020. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 9.0 ppm, in 2019.

What handles it

  • NSF/ANSI 58 look for “Nitrate/Nitrite Reduction”
  • NSF/ANSI 53 look for “Nitrate/Nitrite (30 ppm challenge)”

Arsenic

Comes from the source

Above the health goal

4.0ppb

Highest yearly average, 2020 to 2026

Averaged by year, the highest was 4.0 ppb, in 2026: below EPA’s legal limit of 10 ppb, but above its health goal of zero. That was also the latest year on file.

What handles it

  • NSF/ANSI 58 look for “Arsenic (Pentavalent)<=50 ppb Reduction”
  • NSF/ANSI 53 look for “Arsenic (Pentavalent)<=50 ppb Reduction”

Uranium

Comes from the source

Above the health goal

11.4ppb

Highest yearly average, 2020 to 2026

2026, one sample: 10.9 ppb

Averaged by year, the highest was 11.4 ppb, in 2020: below EPA’s legal limit of 30 ppb, but above its health goal of zero. In 2026, the latest year on file, its one sample was 10.9 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 12.3 ppb, in 2017.

What handles it

Below EPA’s limits1

Fluoride

Forms or is added in treatment

Below EPA’s limits

0.3ppm

Highest yearly average, 2020 to 2026

2026, one sample: 0.3 ppm

Averaged by year, the highest was 0.3 ppm, in 2020, below EPA’s legal limit of 4.0 ppm. In 2026, the latest year on file, its one sample was 0.3 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.3 ppm, in 2014.

What handles it

4 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Chromium (total)
  • Haloacetic acids (HAA5)
  • Lead
  • Total trihalomethanes (TTHM)

What handles it

A certification covers specific claims, not a whole standard. Look for these claims on the certifier’s listing, not the box. Wording varies a little: NSF writes “Lead Reduction,” WQA just “Lead.”

  • NSF/ANSI 53

    Claims: Nitrate/Nitrite (30 ppm challenge), Arsenic (Pentavalent)<=50 ppb Reduction

    For: Nitrate, Arsenic

    Other certifiers’ wording: Arsenic (III) (50 ppb influent level)

  • NSF/ANSI 58

    Claims: Nitrate/Nitrite Reduction, Arsenic (Pentavalent)<=50 ppb Reduction, Uranium

    For: Nitrate, Arsenic, Uranium

    Other certifiers’ wording: Nitrate; Arsenic (Pentavalent)<=300 ppb Reduction; Arsenic (V) (300 ppb influent level)

At the tap, or for the whole house?

These come with the water itself, so a whole-house system certified for the same claims treats every tap and shower. A filter at the tap treats drinking water for much less. How whole-house systems compare.

Filters with those claims on a certifier’s listing

Disclosure: TapBuff earns a commission if you buy through some links on this page. It does not change which standard or filter we name. As an Amazon Associate, TapBuff earns from qualifying purchases. How TapBuff makes money

Compare five-year costs

The best reverse osmosis systems, ranked

Hardness

Very hard, 325 mg/L (19 grains per gallon), at its one sampling point, 2020 to 2026.

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.

Softeners compared at 19 grains per gallon, salt includedSoftener or salt-free conditioner?California water hardness, utility by utility

Violations since 2016

Contaminant or ruleTypePeriodMeasuredStatus
Lead and Copper Rule RevisionsThe required inventory of lead service lines was not completed or submitted on time.EPA: LSL InventoryOct. 17, 2024—Unaddressed
Revised Total Coliform RuleE. coli was confirmed in the water system.EPA: Maximum Contaminant Level Violation, E. coli (RTCR)June 1, 2023 to June 30, 2023—Resolved
Revised Total Coliform RuleE. coli was confirmed in the water system.EPA: Maximum Contaminant Level Violation, E. coli (RTCR)Aug. 1, 2022 to Aug. 31, 2022—Resolved
Revised Total Coliform RuleE. coli was confirmed in the water system.EPA: Maximum Contaminant Level Violation, E. coli (RTCR)May 1, 2022 to May 31, 2022—Resolved
Health-based violations only. Resolved and archived mean the utility returned to compliance or the state closed the record. 6 monitoring or reporting violations not shown.

What this report can’t tell you

  • Everything else. Nitrate, arsenic, uranium, fluoride, chromium (total), 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. Del Norte Mutual Water Co.’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 Jan. 31, 2020 to May 13, 2026.

Testing your own tap

Del Norte Mutual Water Co.’s results are for the water it sends out. What your own service line, solder and fixtures add shows up only in a test of your tap, by a lab California certifies.

The 3 labs California certifies closest to the area Del Norte 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.

    Santa Paula, CA · about 3 miles

    Certified for bacteria, nitrate, lead and copper, metals, minerals and other inorganics, organic chemicals, disinfection byproducts, radioactivity

    (805) 392-2000

  • Ventura County Public Health Laboratory

    Oxnard, CA · about 8 miles

    Certified for bacteria

    (805) 981-5131

  • Camrosa Water District Wastewater Laboratory

    Camarillo, CA · about 9 miles

    Certified for bacteria

    (805) 248-0402

All 145 certified labs for California

Sources

PWSID CA5602104. Rebuilt from EPA data on Oct. 18, 2026.

Towns it serves

Also in Ventura County

All California utilities

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