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U.S.N., San Nicolas Island

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
187 people
Connections
106
Water source
Groundwater influenced by surface water
Based in
Point Mugu, CA
County
Ventura
Owner
Federal government

The short answer

1 result is above the limit’s level with no violation recorded, and 1 more is above the health goal. The worst: Arsenic, above the limit’s level, no violation. No health-based violations on file since 2016.

What handles it

What was found

Arsenic, nitrate, total trihalomethanes (TTHM), haloacetic acids (HAA5), fluoride and chromium (total): California’s own results, samples taken from Jan. 14, 2020 to April 6, 2026, with EPA’s 2012 to 2019 file for earlier years.

Above the limit’s level, no violation recorded1

Arsenic

Comes from the source

Above the limit’s level, no violation

40ppb

Highest yearly average, 2020 to 2026

Averaged by year, the highest was 40 ppb, in 2026, about 4 times EPA’s legal limit of 10 ppb. Its highest single sample was 80 ppb. That was also the latest year on file. EPA judges this limit on running averages at each sampling point, and recorded no violation for arsenic at this utility since 2020. Results like these with no violation often include water sampled before treatment or blending; the utility’s annual report says what reaches the tap. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 46.5 ppb, in 2014.

What handles it

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

Above the health goal1

Nitrate

Comes from the source

Above the health goal

21.8ppm

Highest sample; found in 7 of 15

2026 average: 0.75 ppm

One sample, in 2020, was above EPA’s legal limit of 10 ppm, at 21.8 ppm. No follow-up sample at that point within 30 days is on file. 10 ppm is also EPA’s health goal. In 2026, the latest year on file, its two samples averaged 0.75 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 15.2 ppm, in 2017.

What handles it

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

Below EPA’s limits4

Total trihalomethanes (TTHM)

Forms or is added in treatment

Below EPA’s limits

69ppb

Highest yearly average, 2020 to 2026

2026 average: 21.8 ppb

Averaged by year, the highest was 69 ppb, in 2020, below EPA’s legal limit of 80 ppb. Its highest single sample was 106 ppb. In 2026, the latest year on file, its five samples averaged 21.8 ppb. EPA recorded no violation for total trihalomethanes (TTHM) at this utility since 2020. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 49 ppb, in 2019.

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

Below EPA’s limits

17ppb

Highest yearly average, 2020 to 2026

2026 average: 3.0 ppb

Averaged by year, the highest was 17 ppb, in 2020, below EPA’s legal limit of 60 ppb. Its highest single sample was 20 ppb. In 2026, the latest year on file, its four samples averaged 3.0 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 7.3 ppb, in 2019.

What handles it

No certification claim covers this compound yet.

Fluoride

Forms or is added in treatment

Below EPA’s limits

0.55ppm

Highest yearly average, 2020 to 2026

Averaged by year, the highest was 0.55 ppm, in 2026, below EPA’s legal limit of 4.0 ppm. Its highest single sample was 1.1 ppm. That was also the latest year on file. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.05 ppm, in 2017.

What handles it

Chromium (total)

Comes from the source

Below EPA’s limits

10ppb

Highest yearly average, 2020 to 2026

2026 average: 7.0 ppb

Averaged by year, the highest was 10 ppb, in 2020, below EPA’s legal limit of 100 ppb. Its highest single sample was 20 ppb. In 2026, the latest year on file, its two samples averaged 7.0 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 9.5 ppb, in 2017.

What handles it

One compound tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Lead

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

    For: Arsenic, Nitrate

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

  • NSF/ANSI 58

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

    For: Arsenic, Nitrate

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

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

Violations since 2016

No health-based violations on file with EPA since 2016.

What this report can’t tell you

  • Everything else. Arsenic, nitrate, total trihalomethanes (TTHM), haloacetic acids (HAA5), fluoride and chromium (total) results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. U.S.N., San Nicolas Island’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. 14, 2020 to April 6, 2026.

Testing your own tap

U.S.N., San Nicolas Island’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.

No lab California certifies is within 75 miles of the area U.S.N., San Nicolas Island serves on the state’s list. Some take samples by mail; the state’s page lists them all.

All 145 certified labs for California

Sources

PWSID CA5610702. Rebuilt from EPA data on Oct. 18, 2026.

Also in Ventura County

All California utilities

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