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Mariposa Public Utility Dist

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
2,000 people
Connections
684
Water source
Surface water
Based in
Mariposa, CA
County
Mariposa
Owner
Local government
Hardness
Varies by source
The ZIP code it serves

95338

The short answer

1 result is above the limit’s level with no violation recorded. The worst: Total trihalomethanes (TTHM), above the limit’s level, no violation. 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 1.5 ppm, for the period ending Dec. 31, 1998. None since is on file, so it is not counted as a current finding.

Total trihalomethanes (TTHM), haloacetic acids (HAA5), nitrate, fluoride, arsenic and chromium (total): California’s own results, samples taken from Feb. 19, 2020 to June 17, 2026, with EPA’s 2012 to 2019 file for earlier years.

Uranium: EPA’s compliance monitoring file, samples taken from July 23, 2014 to Aug. 12, 2015. Newer results are in the utility’s annual water quality report.

Above the limit’s level, no violation recorded1

Total trihalomethanes (TTHM)

Forms or is added in treatment

Above the limit’s level, no violation

86.3ppb

Highest yearly average, 2020 to 2026

2026 average: 31.5 ppb

Averaged by year, the highest was 86.3 ppb, in 2021, above EPA’s legal limit of 80 ppb. Its highest single sample was 140 ppb. In 2026, the latest year on file, its two samples averaged 31.5 ppb. EPA judges this limit on running averages at each sampling point, and recorded no violation for total trihalomethanes (TTHM) 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 70.3 ppb, in 2018, and EPA recorded violations in 2012 and 2013.

What handles it

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

Below EPA’s limits3

Haloacetic acids (HAA5)

Forms or is added in treatment

Below EPA’s limits

42.3ppb

Highest yearly average, 2020 to 2026

2026 average: 20 ppb

Averaged by year, the highest was 42.3 ppb, in 2021, below EPA’s legal limit of 60 ppb. Its highest single sample was 100 ppb. In 2026, the latest year on file, its two samples averaged 20 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 42.3 ppb, in 2016, and EPA recorded a violation in 2012.

What handles it

No certification claim covers this compound yet.

Nitrate

Comes from the source

Below EPA’s limits

2.5ppm

Highest sample; found in 28 of 42

2026 average: 0.77 ppm

The highest sample, in 2024, was 2.5 ppm, below EPA’s legal limit of 10 ppm. In 2026, the latest year on file, its six samples averaged 0.77 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 3.0 ppm, in 2017.

What handles it

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

Fluoride

Forms or is added in treatment

Below EPA’s limits

0.022ppm

Highest yearly average, 2020 to 2026

2026: not found

Averaged by year, the highest was 0.022 ppm, in 2024, below EPA’s legal limit of 4.0 ppm. Its highest single sample was 0.11 ppm. In 2026, the latest year on file, it wasn’t found in any of its three samples.

What handles it

4 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Arsenic
  • Chromium (total)
  • 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: Trihalomethanes (TTHM) Reduction

    For: Total trihalomethanes (TTHM)

    Other certifiers’ wording: VOC Reduction

  • NSF/ANSI 58

    Claim: Trihalomethanes (TTHM) Reduction

    For: Total trihalomethanes (TTHM)

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

Hardness

Soft to very hard depending on the source, 7.9 to 260 mg/L (0.5 to 15.2 grains per gallon), across 6 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. Total trihalomethanes (TTHM), haloacetic acids (HAA5), nitrate, fluoride, arsenic and chromium (total) results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Uranium comes from EPA’s file alone, which ends in 2019. Mariposa Public Utility Dist’s own annual report, which it must send you every year, has newer results for those and 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 Feb. 19, 2020 to June 17, 2026; EPA’s compliance samples are from July 23, 2014 to Aug. 12, 2015.

Testing your own tap

Mariposa Public Utility Dist’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 Mariposa Public Utility Dist serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.

  • Precision Enviro-Tech

    Twain Harte, CA · about 39 miles

    Certified for bacteria

    (209) 477-8105

  • Microbac Laboratories, Inc. - Turlock

    Turlock, CA · about 49 miles

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

    (707) 822-4649

  • SGS North America, Inc.

    Clovis, CA · about 49 miles

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

    (559) 862-2118

All 145 certified labs for California

Sources

PWSID CA2210001. Rebuilt from EPA data on Oct. 18, 2026.

Towns it serves

Also in Mariposa County

All California utilities

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