Skip to content
TapBuff
ZIP

Sandmound 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
100 people
Connections
110
Water source
Groundwater
Based in
Bethel Island, CA
County
Contra Costa
Owner
Private
Hardness
Very hard
The ZIP code it serves

94511

The short answer

1 result is above EPA’s legal limit, and 1 more is above the limit’s level with no violation recorded. The worst: Copper, above the action level. 1 health-based violation since 2016.

What handles it

What was found

Lead and copper: EPA SDWIS monitoring periods ending 2024.

Arsenic, fluoride, chromium (total), nitrate and total trihalomethanes (TTHM): California’s own results, samples taken from June 22, 2020 to June 18, 2026, with EPA’s 2012 to 2019 file for earlier years.

Above the legal limit1

Copper

Comes from pipes, often your own

Above the action level

1.5ppm

90th percentile, 2022 to 2024

In the latest period, 9 in 10 homes sampled were at or below 1.5 ppm, above EPA’s action level of 1.3 ppm.

What handles it

Above the limit’s level, no violation recorded1

Arsenic

Comes from the source

Above the limit’s level, no violation

14.2ppb

Highest yearly average, 2021 to 2026

2026 average: 9.7 ppb

Averaged by year, the highest was 14.2 ppb, in 2022, above EPA’s legal limit of 10 ppb. Its highest single sample was 38 ppb. In 2026, the latest year on file, its three samples averaged 9.7 ppb. EPA judges this limit on running averages at each sampling point, and recorded no violation for arsenic 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 8.0 ppb, in 2012.

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 limits1

Fluoride

Forms or is added in treatment

Below EPA’s limits

0.12ppm

Highest yearly average, 2021 to 2024

Averaged by year, the highest was 0.12 ppm, in 2024, below EPA’s legal limit of 4.0 ppm. Its highest single sample was 0.13 ppm. That was also the latest year on file. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.1 ppm, in 2012.

What handles it

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

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: Copper Reduction, Arsenic (Pentavalent)<=50 ppb Reduction

    For: Copper, Arsenic

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

  • NSF/ANSI 58

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

    For: Copper, Arsenic

    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

Hardness

Very hard, typically 305 mg/L (17.8 grains per gallon), across 2 sampling points, 2021 to 2024.

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 17.8 grains per gallon, salt includedSoftener or salt-free conditioner?California water hardness, utility by utility

Violations since 2016

Contaminant or ruleTypePeriodMeasuredStatus
Lead and Copper Rule RevisionsThe required inventory of lead service lines was not completed or submitted on time.EPA: LSL InventoryOct. 17, 2024—Unaddressed
Health-based violations only. Resolved and archived mean the utility returned to compliance or the state closed the record. 3 monitoring or reporting violations not shown.

What this report can’t tell you

  • Everything else. Arsenic, fluoride, chromium (total), nitrate and total trihalomethanes (TTHM) results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Sandmound 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 June 22, 2020 to June 18, 2026.

Testing your own tap

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

  • McCampbell Analytical, Inc.

    Pittsburg, CA · about 15 miles

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

    (925) 252-9262

  • Precision Enviro-Tech

    Stockton, CA · about 20 miles

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

    (209) 405-0601

  • San Joaquin County Public Health Laboratory

    Stockton, CA · about 21 miles

    Certified for bacteria

    (209) 468-3460

All 145 certified labs for California

Sources

PWSID CA0707556. Rebuilt from EPA data on Oct. 18, 2026.

Towns it serves

Also in Contra Costa County

All California utilities

What to do next