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White Mountain 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
142 people
Connections
43
Water source
Groundwater
Based in
Bishop, CA
County
Mono
Owner
Private
Hardness
Moderately hard

The short answer

2 results are 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

Arsenic, uranium, fluoride, chromium (total) and nitrate: California’s own results, samples taken from Aug. 25, 2020 to Dec. 16, 2025, with EPA’s 2012 to 2019 file for earlier years.

Above the health goal2

Arsenic

Comes from the source

Above the health goal

3.0ppb

Highest yearly average, 2022 to 2025

2025, one sample: 2.7 ppb

Averaged by year, the highest was 3.0 ppb, in 2022: below EPA’s legal limit of 10 ppb, but above its health goal of zero. In 2025, the latest year on file, its one sample was 2.7 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 2.0 ppb, in 2019.

What handles it

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

Uranium

Comes from the source

Above the health goal

2.3ppb

Highest yearly average, 2022

Averaged by year, the highest was 2.3 ppb, in 2022: below EPA’s legal limit of 30 ppb, but above its health goal of zero. That is the only year on file. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 4.6 ppb, in 2019.

What handles it

Below EPA’s limits1

Fluoride

Forms or is added in treatment

Below EPA’s limits

0.6ppm

Highest yearly average, 2022 to 2025

2025, one sample: 0.55 ppm

Averaged by year, the highest was 0.6 ppm, in 2022, below EPA’s legal limit of 4.0 ppm. In 2025, the latest year on file, its one sample was 0.55 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.4 ppm, in 2019.

What handles it

3 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Chromium (total)
  • Lead
  • 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

    Claim: Arsenic (Pentavalent)<=50 ppb Reduction

    For: Arsenic

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

  • NSF/ANSI 58

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

    For: Arsenic, Uranium

    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, 110 mg/L (6.4 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 6.4 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. Arsenic, uranium, fluoride, chromium (total) and nitrate results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. White Mountain 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 Aug. 25, 2020 to Dec. 16, 2025.

Testing your own tap

White Mountain 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.

No lab California certifies is within 75 miles of the area White Mountain Mutual Water Company serves on the state’s list. Some take samples by mail; the state’s page lists them all.

All 145 certified labs for California

Sources

PWSID CA2600621. Rebuilt from EPA data on Oct. 18, 2026.

Also in Mono County

All California utilities

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