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Callender Grove Mutual Water

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
116 people
Connections
37
Water source
Groundwater
Based in
San Luis Obispo, CA
County
San Luis Obispo
Owner
Private
Hardness
Varies by source
The ZIP code it serves

93420

The short answer

Nothing in EPA’s and California’s records for this utility is above a health goal. That covers nitrate, arsenic and other regulated chemicals, plus lead and copper, not everything. No health-based violations on file since 2016.

What was found

Nitrate, chromium (total), fluoride, total trihalomethanes (TTHM), arsenic and haloacetic acids (HAA5): California’s own results, samples taken from Feb. 12, 2020 to April 22, 2026, with EPA’s 2012 to 2019 file for earlier years.

Below EPA’s limits4

Nitrate

Comes from the source

Below EPA’s limits

5.7ppm

Highest sample; found in 32 of 32

2026 average: 5.0 ppm

The highest sample, in 2026, was 5.7 ppm, below EPA’s legal limit of 10 ppm. That was also the latest year on file, and its four samples averaged 5.0 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 4.9 ppm, in 2018.

What handles it

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

Chromium (total)

Comes from the source

Below EPA’s limits

6.8ppb

Highest yearly average, 2021 to 2024

2024: not found

Averaged by year, the highest was 6.8 ppb, in 2021, below EPA’s legal limit of 100 ppb. Its highest single sample was 8.8 ppb. In 2024, the latest year on file, it wasn’t found in any of its two samples.

What handles it

Fluoride

Forms or is added in treatment

Below EPA’s limits

0.15ppm

Highest yearly average, 2021 to 2024

2024 average: 0.14 ppm

Averaged by year, the highest was 0.15 ppm, in 2021, below EPA’s legal limit of 4.0 ppm. Its highest single sample was 0.19 ppm. In 2024, the latest year on file, its two samples averaged 0.14 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.2 ppm, in 2012.

What handles it

Total trihalomethanes (TTHM)

Forms or is added in treatment

Below EPA’s limits

2.9ppb

Highest yearly average, 2021 to 2024

2024: not found

Averaged by year, the highest was 2.9 ppb, in 2021, below EPA’s legal limit of 80 ppb. In 2024, the latest year on file, it wasn’t found in any of its three samples.

What handles it

  • NSF/ANSI 53 look for “Trihalomethanes (TTHM) Reduction”
  • NSF/ANSI 58 look for “Trihalomethanes (TTHM) Reduction”
3 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Arsenic
  • Haloacetic acids (HAA5)
  • Lead

Hardness

Moderately hard to very hard depending on the source, 67 to 235 mg/L (3.9 to 13.7 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, 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. There is 1 monitoring or reporting violation: a sample missed, late or not reported.

What this report can’t tell you

  • Everything else. Nitrate, chromium (total), fluoride, total trihalomethanes (TTHM), arsenic and haloacetic acids (HAA5) results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Callender Grove Mutual Water’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 Feb. 12, 2020 to April 22, 2026.

Testing your own tap

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

  • County of San Luis Obispo Public Health Laboratory

    San Luis Obispo, CA · about 12 miles

    Certified for bacteria

    (805) 781-5507

  • Fruit Growers Laboratory, Inc.

    San Luis Obispo, CA · about 12 miles

    Certified for bacteria

    (805) 783-2940

  • Abalone Coast Analytical, Inc.

    San Luis Obispo, CA · about 12 miles

    Certified for bacteria

    (805) 595-1080

All 145 certified labs for California

Sources

PWSID CA4000805. Rebuilt from EPA data on Oct. 18, 2026.

Also in San Luis Obispo County

All California utilities

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