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Coast Springs - Cal. Water Service (Puc)

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
445 people
Connections
249
Water source
Surface water
Based in
San Jose, CA
County
Marin
Owner
Private
Hardness
Varies by source
The ZIP code it serves

94929

The short answer

1 result is above the health goal. The worst: Arsenic, above the health goal. No health-based violations on file since 2016.

What handles it

What was found

Copper: EPA’s file records a utility’s copper only when it exceeds the action level. The last here was 1.8 ppm, for the period ending Dec. 31, 2006. None since is on file, so it is not counted as a current finding.

Arsenic, nitrate, haloacetic acids (HAA5), total trihalomethanes (TTHM), fluoride, chromium (total) and uranium: California’s own results, samples taken from Jan. 20, 2020 to June 24, 2026, with EPA’s 2012 to 2019 file for earlier years.

Above the health goal1

Arsenic

Comes from the source

Above the health goal

0.83ppb

Highest yearly average, 2020 to 2026

2026: not found

Averaged by year, the highest was 0.83 ppb, in 2023: below EPA’s legal limit of 10 ppb, but above its health goal of zero. Its highest single sample was 8.1 ppb. In 2026, the latest year on file, it wasn’t found in any of its 11 samples. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 1.6 ppb, in 2016.

What handles it

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

Below EPA’s limits5

Nitrate

Comes from the source

Below EPA’s limits

6.1ppm

Highest sample; found in 126 of 191

2026 average: 0.95 ppm

The highest sample, in 2020, was 6.1 ppm, below EPA’s legal limit of 10 ppm. In 2026, the latest year on file, its 16 samples averaged 0.95 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 13.8 ppm, in 2013.

What handles it

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

Haloacetic acids (HAA5)

Forms or is added in treatment

Below EPA’s limits

27.7ppb

Highest yearly average, 2020 to 2026

2026 average: 11.8 ppb

Averaged by year, the highest was 27.7 ppb, in 2023, below EPA’s legal limit of 60 ppb. Its highest single sample was 79 ppb. In 2026, the latest year on file, its four samples averaged 11.8 ppb. EPA recorded no violation for haloacetic acids (HAA5) at this utility since 2020. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 44 ppb, in 2017.

What handles it

No certification claim covers this compound yet.

Total trihalomethanes (TTHM)

Forms or is added in treatment

Below EPA’s limits

35.6ppb

Highest yearly average, 2020 to 2026

2026 average: 18.2 ppb

Averaged by year, the highest was 35.6 ppb, in 2024, below EPA’s legal limit of 80 ppb. Its highest single sample was 116 ppb. In 2026, the latest year on file, its six samples averaged 18.2 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 31.4 ppb, in 2013.

What handles it

  • NSF/ANSI 53 look for “Trihalomethanes (TTHM) Reduction”
  • NSF/ANSI 58 look for “Trihalomethanes (TTHM) Reduction”

Fluoride

Forms or is added in treatment

Below EPA’s limits

0.14ppm

Highest yearly average, 2020 to 2026

2026 average: 0.1 ppm

Averaged by year, the highest was 0.14 ppm, in 2023, below EPA’s legal limit of 4.0 ppm. Its highest single sample was 0.26 ppm. In 2026, the latest year on file, its seven samples averaged 0.1 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.18 ppm, in 2012.

What handles it

Chromium (total)

Comes from the source

Below EPA’s limits

0.46ppb

Highest yearly average, 2020 to 2026

2026: not found

Averaged by year, the highest was 0.46 ppb, in 2022, below EPA’s legal limit of 100 ppb. Its highest single sample was 2.0 ppb. In 2026, the latest year on file, it wasn’t found in any of its six samples.

What handles it

2 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Lead
  • Uranium

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

    Claim: Arsenic (Pentavalent)<=50 ppb Reduction

    For: Arsenic

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

  • NSF/ANSI 58

    Claim: Arsenic (Pentavalent)<=50 ppb Reduction

    For: Arsenic

    Other certifiers’ wording: 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

Moderately hard to hard depending on the source, 77 to 130 mg/L (4.5 to 7.6 grains per gallon), across 11 sampling points, 2019 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, 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. Arsenic, nitrate, haloacetic acids (HAA5), total trihalomethanes (TTHM), fluoride, chromium (total) and uranium results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Coast Springs - Cal. Water Service (Puc)’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. 20, 2020 to June 24, 2026.

Testing your own tap

Coast Springs - Cal. Water Service (Puc)’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 Coast Springs - Cal. Water Service (Puc) serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.

  • Alpha Analytical Laboratories Inc. - North Bay

    Petaluma, CA · about 17 miles

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

    (707) 769-3128

  • Brelje and Race Laboratories, Inc.

    Santa Rosa, CA · about 19 miles

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

    (707) 544-8807

  • K Prime, LLC.

    Santa Rosa, CA · about 20 miles

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

    (707) 527-7574

All 145 certified labs for California

Sources

PWSID CA2110007. Rebuilt from EPA data on Oct. 18, 2026.

Towns it serves

Also in Marin County

All California utilities

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