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Mark West Acres MWC

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
61 people
Connections
22
Water source
Groundwater
Based in
Santa Rosa, CA
County
Sonoma
Owner
Private
Hardness
Hard
The ZIP code it serves

95404

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, chromium (total) and fluoride: California’s own results, samples taken from March 27, 2020 to March 18, 2026, with EPA’s 2012 to 2019 file for earlier years.

Below EPA’s limits1

Nitrate

Comes from the source

Below EPA’s limits

0.42ppm

Highest sample; found in 1 of 7

2026: not found

The highest sample, in 2020, was 0.42 ppm, below EPA’s legal limit of 10 ppm. In 2026, 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)”
4 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Arsenic
  • Chromium (total)
  • Fluoride
  • Lead

Hardness

Hard, 160 mg/L (9.4 grains per gallon), at its one sampling point, 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.

Softeners compared at 9.4 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 2020 on, with EPA’s national file for 2012 to 2019. Mark West Acres MWC’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 March 27, 2020 to March 18, 2026.

Testing your own tap

Mark West Acres MWC’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 Mark West Acres MWC serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.

  • Sonoma County Public Health Laboratory

    Santa Rosa, CA · about 4 miles

    Certified for bacteria

    (707) 565-4711

  • K Prime, LLC.

    Santa Rosa, CA · about 6 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 6 miles

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

    (707) 544-8807

All 145 certified labs for California

Sources

PWSID CA4900605. Rebuilt from EPA data on Oct. 18, 2026.

Also in Sonoma County

All California utilities

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