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Gran Cielo 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
139 people
Connections
42
Water source
Groundwater
Based in
San Simeon, CA
County
San Luis Obispo
Owner
Private
Hardness
Varies by source

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: Lead, above the action level. No health-based violations on file since 2016.

What handles it

What was found

Lead and copper: EPA SDWIS monitoring periods ending 2026.

Arsenic, total trihalomethanes (TTHM), haloacetic acids (HAA5), nitrate, fluoride and chromium (total): California’s own results, samples taken from Feb. 15, 2022 to June 16, 2026.

Above the legal limit1

Lead

Comes from pipes, often your own

Above the action level

21ppb

90th percentile, 2026

In the latest period, 9 in 10 homes sampled were at or below 21 ppb, above EPA’s action level of 15 ppb. The action level drops to 10 ppb on Nov. 1, 2027, and this result is at or above that. EPA’s health goal for lead is zero.

What handles it

Above the limit’s level, no violation recorded1

Arsenic

Comes from the source

Above the limit’s level, no violation

40ppb

Highest yearly average, 2022 to 2026

2026 average: 8.5 ppb

Averaged by year, the highest was 40 ppb, in 2022, about 4 times EPA’s legal limit of 10 ppb. Its highest single sample was 50 ppb. In 2026, the latest year on file, its 10 samples averaged 8.5 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.

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 limits4

Total trihalomethanes (TTHM)

Forms or is added in treatment

Below EPA’s limits

39ppb

Highest yearly average, 2024 to 2025

2025 average: 3.3 ppb

Averaged by year, the highest was 39 ppb, in 2024, below EPA’s legal limit of 80 ppb. In 2025, the latest year on file, its three samples averaged 3.3 ppb.

What handles it

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

Haloacetic acids (HAA5)

Forms or is added in treatment

Below EPA’s limits

10ppb

Highest yearly average, 2024 to 2025

2025: not found

Averaged by year, the highest was 10 ppb, in 2024, below EPA’s legal limit of 60 ppb. In 2025, the latest year on file, it wasn’t found in its one sample.

What handles it

No certification claim covers this compound yet.

Nitrate

Comes from the source

Below EPA’s limits

1.4ppm

Highest sample; found in 5 of 10

2026 average: 0.6 ppm

The highest sample, in 2024, was 1.4 ppm, below EPA’s legal limit of 10 ppm. In 2026, the latest year on file, its two samples averaged 0.6 ppm.

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

0.27ppm

Highest yearly average, 2022 to 2025

2025 average: 0.24 ppm

Averaged by year, the highest was 0.27 ppm, in 2022, below EPA’s legal limit of 4.0 ppm. Its highest single sample was 0.33 ppm. In 2025, the latest year on file, its two samples averaged 0.24 ppm.

What handles it

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

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

    For: Lead, Arsenic

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

  • NSF/ANSI 58

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

    For: Lead, 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 water filters for lead, ranked

The best reverse osmosis systems, ranked

Hardness

Moderately hard to hard depending on the source, 91 to 135 mg/L (5.3 to 7.9 grains per gallon), across 2 sampling points, 2022 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, 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, total trihalomethanes (TTHM), haloacetic acids (HAA5), nitrate, fluoride and chromium (total) results here are California’s own from 2022 on, with EPA’s national file for 2012 to 2019. Gran Cielo 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 Feb. 15, 2022 to June 16, 2026.

Testing your own tap

Gran Cielo 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 Gran Cielo 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 CA4000853. Rebuilt from EPA data on Oct. 18, 2026.

Towns it serves

Also in San Luis Obispo County

All California utilities

What to do next