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Loma Mar Mutual

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
65 people
Connections
34
Water source
Surface water
Based in
Loma Mar, CA
County
San Mateo
Owner
Private
Hardness
Very hard
The ZIP code it serves

94021

The short answer

2 results are above the health goal. The worst: Arsenic, above the health goal. 2 health-based violations since 2016.

What handles it

What was found

Lead and copper: EPA SDWIS monitoring periods ending 2007 to 2026.

Arsenic, total trihalomethanes (TTHM), chromium (total), haloacetic acids (HAA5), fluoride and nitrate: California’s own results, samples taken from Jan. 8, 2020 to June 9, 2026, with EPA’s 2012 to 2019 file for earlier years.

Above the health goal2

Arsenic

Comes from the source

Above the health goal

2.7ppb

Highest yearly average, 2020 to 2025

2025: not found

Averaged by year, the highest was 2.7 ppb, in 2023: below EPA’s legal limit of 10 ppb, but above its health goal of zero. In 2025, the latest year on file, it wasn’t found in its one sample. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 2.1 ppb, in 2018.

What handles it

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

Lead

Comes from pipes, often your own

Above the health goal

2.8ppb

90th percentile, 2024 to 2026

In the latest period, 9 in 10 homes sampled were at or below 2.8 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 limits4

Total trihalomethanes (TTHM)

Forms or is added in treatment

Below EPA’s limits

37.2ppb

Highest yearly average, 2020 to 2026

2026 average: 9.9 ppb

Averaged by year, the highest was 37.2 ppb, in 2021, below EPA’s legal limit of 80 ppb. Its highest single sample was 170 ppb. In 2026, the latest year on file, its 15 samples averaged 9.9 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 189 ppb, in 2014, and EPA recorded a violation in 2016.

What handles it

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

Chromium (total)

Comes from the source

Below EPA’s limits

17ppb

Highest yearly average, 2020 to 2025

2025: not found

Averaged by year, the highest was 17 ppb, in 2023, below EPA’s legal limit of 100 ppb. In 2025, the latest year on file, it wasn’t found in its one sample.

What handles it

Haloacetic acids (HAA5)

Forms or is added in treatment

Below EPA’s limits

9.9ppb

Highest yearly average, 2020 to 2026

2026 average: 9.0 ppb

Averaged by year, the highest was 9.9 ppb, in 2022, below EPA’s legal limit of 60 ppb. Its highest single sample was 20.9 ppb. In 2026, the latest year on file, its two samples averaged 9.0 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 95.8 ppb, in 2012.

What handles it

No certification claim covers this compound yet.

Fluoride

Forms or is added in treatment

Below EPA’s limits

0.29ppm

Highest yearly average, 2020 to 2025

2025, one sample: 0.15 ppm

Averaged by year, the highest was 0.29 ppm, in 2023, below EPA’s legal limit of 4.0 ppm. In 2025, the latest year on file, its one sample was 0.15 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.27 ppm, 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.
  • Nitrate

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, Lead Reduction

    For: Arsenic, Lead

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

  • NSF/ANSI 58

    Claims: Arsenic (Pentavalent)<=50 ppb Reduction, Lead Reduction

    For: Arsenic, Lead

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

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 reverse osmosis systems, ranked

The best water filters for lead, ranked

Hardness

Very hard, 250 mg/L (14.6 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 14.6 grains per gallon, salt includedSoftener or salt-free conditioner?California water hardness, utility by utility

Violations since 2016

Contaminant or ruleTypePeriodMeasuredStatus
Surface Water Treatment RuleRequired treatment for surface water or groundwater was not met.EPA: Treatment Technique (SWTR and GWR)Aug. 1, 2016 to Aug. 31, 2016—Resolved
TTHMThe running average was above the legal limit.EPA: Maximum Contaminant Level Violation, AverageApril 1, 2016 to June 30, 20160.15 MG/LResolved
Health-based violations only. Resolved and archived mean the utility returned to compliance or the state closed the record.

What this report can’t tell you

  • Everything else. Arsenic, total trihalomethanes (TTHM), chromium (total), haloacetic acids (HAA5), fluoride and nitrate results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Loma Mar Mutual’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. 8, 2020 to June 9, 2026.

Testing your own tap

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

  • San Mateo County Public Health Laboratory

    San Mateo, CA · about 18 miles

    Certified for bacteria

    (650) 573-2500

  • Eurofins Built Environment Testing West-Burlingame

    Burlingame, CA · about 22 miles

    Certified for bacteria

    (623) 298-1015

  • Garratt-Callahan Laboratory

    Burlingame, CA · about 23 miles

    Certified for nitrate, metals, minerals and other inorganics

    (650) 697-5811

All 145 certified labs for California

Sources

PWSID CA4100512. Rebuilt from EPA data on Oct. 18, 2026.

Towns it serves

Also in San Mateo County

All California utilities

What to do next