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Larkin Woods Mutual Water Company

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
34 people
Connections
18
Water source
Groundwater influenced by surface water
Based in
Sebastopol, CA
County
Sonoma
Owner
Private
Hardness
Soft
The ZIP code it serves

95472

The short answer

1 result is above EPA’s legal limit, and 1 more is above the health goal. The worst: Copper, above the action level. No health-based violations on file since 2016.

What handles it

What was found

Lead and copper: EPA SDWIS monitoring periods ending 2024 to 2026.

Nitrate, arsenic, chromium (total) and fluoride: California’s own results, samples taken from Nov. 15, 2021 to July 10, 2025.

Above the legal limit1

Copper

Comes from pipes, often your own

Above the action level

1.4ppm

90th percentile, 2026

In the latest period, 9 in 10 homes sampled were at or below 1.4 ppm, above EPA’s action level of 1.3 ppm.

What handles it

Above the health goal1

Lead

Comes from pipes, often your own

Above the health goal

2.5ppb

90th percentile, 2026

In the latest period, 9 in 10 homes sampled were at or below 2.5 ppb, below EPA’s action level of 15 ppb. The action level drops to 10 ppb on Nov. 1, 2027. EPA’s health goal for lead is zero.

What handles it

Below EPA’s limits1

Nitrate

Comes from the source

Below EPA’s limits

0.41ppm

Highest sample; found in 1 of 4

2025: not found

The highest sample, in 2021, was 0.41 ppm, below EPA’s legal limit of 10 ppm. In 2025, the latest year on file, it wasn’t found in its one sample.

What handles it

  • NSF/ANSI 58 look for “Nitrate/Nitrite Reduction”
  • NSF/ANSI 53 look for “Nitrate/Nitrite (30 ppm challenge)”
3 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Arsenic
  • Chromium (total)
  • Fluoride

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: Copper Reduction, Lead Reduction

    For: Copper, Lead

  • NSF/ANSI 58

    Claims: Copper Reduction, Lead Reduction

    For: Copper, Lead

At the tap, or for the whole house?

Lead and copper usually come from pipes and fixtures inside or near your home. A whole-house system sits where water enters, so it cannot catch what your own plumbing adds after it. For those, the filter that counts is the one at the tap. 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 water filters for lead, ranked

Hardness

Soft, 54 mg/L (3.2 grains per gallon), at its one sampling point, 2021 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.

Softeners compared at 3.2 grains per gallon, salt includedSoftener or salt-free conditioner?California water hardness, utility by utility

Violations since 2016

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

What this report can’t tell you

  • Everything else. Nitrate, arsenic, chromium (total) and fluoride results here are California’s own from 2021 on, with EPA’s national file for 2012 to 2019. Larkin Woods Mutual Water Company’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 Nov. 15, 2021 to July 10, 2025.

Testing your own tap

Larkin Woods Mutual Water Company’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 Larkin Woods Mutual Water Company serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.

  • K Prime, LLC.

    Santa Rosa, CA · about 8 miles

    Certified for bacteria, nitrate, lead and copper, metals, minerals and other inorganics, PFAS

    (707) 527-7574

  • Brelje and Race Laboratories, Inc.

    Santa Rosa, CA · about 9 miles

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

    (707) 544-8807

  • Sonoma County Public Health Laboratory

    Santa Rosa, CA · about 10 miles

    Certified for bacteria

    (707) 565-4711

All 145 certified labs for California

Sources

PWSID CA4900582. Rebuilt from EPA data on Oct. 18, 2026.

Towns it serves

Also in Sonoma County

All California utilities

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