Skip to content
TapBuff
ZIP

Rim Rock 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
55 people
Connections
25
Water source
Groundwater
Based in
Grover Beach, CA
County
San Luis Obispo
Owner
Private
Hardness
Very hard
The ZIP code it serves

93444

The short answer

1 result is above EPA’s legal limit, and 1 more is above the health goal. The worst: Arsenic, above the legal limit. 31 health-based violations since 2016.

What handles it

What was found

Arsenic, uranium, nitrate, haloacetic acids (HAA5), total trihalomethanes (TTHM), chromium (total) and fluoride: California’s own results, samples taken from Jan. 30, 2020 to May 28, 2026, with EPA’s 2012 to 2019 file for earlier years.

Above the legal limit1

Arsenic

Comes from the source

Above the legal limit

166ppb

Highest yearly average, 2020 to 2026

2026: not found

Averaged by year, the highest was 166 ppb, in 2024, about 17 times EPA’s legal limit of 10 ppb. Its highest single sample was 1,560 ppb. In 2026, the latest year on file, it wasn’t found in any of its seven samples. EPA recorded violations for arsenic at this utility in 2020, 2021, 2022, 2024 and 2025. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 84.7 ppb, in 2017, and EPA recorded violations in 2017, 2018 and 2019.

What handles it

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

Above the health goal1

Uranium

Comes from the source

Above the health goal

14.8ppb

Highest yearly average, 2024 to 2025

Averaged by year, the highest was 14.8 ppb, in 2025: below EPA’s legal limit of 30 ppb, but above its health goal of zero. Its highest single sample was 19.1 ppb. That was also the latest year on file.

What handles it

Below EPA’s limits5

Nitrate

Comes from the source

Below EPA’s limits

6.2ppm

Highest sample; found in 2 of 16

2025: not found

The highest sample, in 2024, was 6.2 ppm, below EPA’s legal limit of 10 ppm. In 2025, the latest year on file, it wasn’t found in any of its two samples.

What handles it

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

Haloacetic acids (HAA5)

Forms or is added in treatment

Below EPA’s limits

15ppb

Highest yearly average, 2020 to 2023

Averaged by year, the highest was 15 ppb, in 2023, below EPA’s legal limit of 60 ppb. That was also the latest year on file.

What handles it

No certification claim covers this compound yet.

Total trihalomethanes (TTHM)

Forms or is added in treatment

Below EPA’s limits

19ppb

Highest yearly average, 2020 to 2025

2025: not found

Averaged by year, the highest was 19 ppb, in 2023, below EPA’s legal limit of 80 ppb. In 2025, the latest year on file, it wasn’t found in any of its two samples.

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

21ppb

Highest yearly average, 2020 to 2024

Averaged by year, the highest was 21 ppb, in 2024, below EPA’s legal limit of 100 ppb. Its highest single sample was 24 ppb. That was also the latest year on file. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 2.0 ppb, in 2013.

What handles it

Fluoride

Forms or is added in treatment

Below EPA’s limits

0.4ppm

Highest yearly average, 2020 to 2024

2024 average: 0.3 ppm

Averaged by year, the highest was 0.4 ppm, in 2020, below EPA’s legal limit of 4.0 ppm. In 2024, the latest year on file, its two samples averaged 0.3 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.49 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.
  • Lead

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

Very hard, typically 559 mg/L (32.7 grains per gallon), across 3 sampling points, 2020 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 32.7 grains per gallon, salt includedSoftener or salt-free conditioner?California water hardness, utility by utility

Violations since 2016

Contaminant or ruleTypePeriodMeasuredStatus
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleApril 1, 2025 to June 30, 202540 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJan. 1, 2025 to March 31, 202540 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleOct. 1, 2024 to Dec. 31, 202464 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJuly 1, 2024 to Sept. 30, 2024163 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleApril 1, 2024 to June 30, 202462 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJan. 1, 2024 to March 31, 2024136 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJan. 1, 2024 to March 31, 2024136 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJuly 1, 2023 to Sept. 30, 20235.0 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleApril 1, 2023 to June 30, 20235.0 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJan. 1, 2023 to March 31, 20235.0 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleOct. 1, 2022 to Dec. 31, 2022136 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJuly 1, 2022 to Sept. 30, 2022136 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleApril 1, 2022 to June 30, 20226.0 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJan. 1, 2022 to March 31, 20224.0 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleOct. 1, 2021 to Dec. 31, 202127 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJuly 1, 2021 to Sept. 30, 202156 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleApril 1, 2021 to June 30, 202156 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJan. 1, 2021 to March 31, 202156 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleOct. 1, 2020 to Dec. 31, 202061 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJuly 1, 2020 to Sept. 30, 202085 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleApril 1, 2020 to June 30, 202028 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJan. 1, 2020 to March 31, 202028 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleOct. 1, 2019 to Dec. 31, 201925 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJuly 1, 2019 to Sept. 30, 201942 UG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleApril 1, 2019 to June 30, 20190.98 MG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJan. 1, 2019 to March 31, 20190.98 MG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleOct. 1, 2018 to Dec. 31, 20180.098 MG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJuly 1, 2018 to Sept. 30, 20180.098 MG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleApril 1, 2018 to June 30, 20180.098 MG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleJan. 1, 2018 to March 31, 20180.1 MG/LResolved
ArsenicA sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single SampleOct. 1, 2017 to Dec. 31, 20170.097 MG/LResolved
Health-based violations only. Resolved and archived mean the utility returned to compliance or the state closed the record. 2 monitoring or reporting violations not shown.

What this report can’t tell you

  • Everything else. Arsenic, uranium, nitrate, haloacetic acids (HAA5), total trihalomethanes (TTHM), chromium (total) and fluoride results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Rim Rock 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 Jan. 30, 2020 to May 28, 2026.

Testing your own tap

Rim Rock 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.

The 3 labs California certifies closest to the area Rim Rock Water Company serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.

  • Oilfield Environmental & Compliance Inc. (OEC)

    Santa Maria, CA · about 6 miles

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

    (805) 922-4772

  • Abalone Coast Analytical, Inc.

    San Luis Obispo, CA · about 17 miles

    Certified for bacteria

    (805) 595-1080

  • Fruit Growers Laboratory, Inc.

    San Luis Obispo, CA · about 18 miles

    Certified for bacteria

    (805) 783-2940

All 145 certified labs for California

Sources

PWSID CA4000750. Rebuilt from EPA data on Oct. 18, 2026.

Towns it serves

Also in San Luis Obispo County

All California utilities

What to do next