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San Miguelito MWC

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
1,600 people
Connections
690
Water source
Surface water bought from another system
Based in
Avila Beach, CA
County
San Luis Obispo
Owner
Private
Hardness
Very hard
The ZIP code it serves

93424

The short answer

2 results are above EPA’s legal limit, and 1 more is above the health goal. The worst: Copper, above the action level. 2 health-based violations since 2016.

What handles it

What was found

Lead and copper: EPA SDWIS monitoring periods ending 1998 to 2025.

Total trihalomethanes (TTHM), arsenic, haloacetic acids (HAA5), nitrate, fluoride and chromium (total): California’s own results, samples taken from Jan. 13, 2020 to May 6, 2026, with EPA’s 2012 to 2019 file for earlier years.

Above the legal limit2

Copper

Comes from pipes, often your own

Above the action level

1.5ppm

90th percentile, 2023 to 2025

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

Total trihalomethanes (TTHM)

Forms or is added in treatment

Above the legal limit

75ppb

Highest yearly average, 2020 to 2026

2026 average: 27.5 ppb

Averaged by year, the highest was 75 ppb, in 2025, below EPA’s legal limit of 80 ppb. Its highest single sample was 150 ppb. In 2026, the latest year on file, its two samples averaged 27.5 ppb. EPA judges this limit at each sampling point, and recorded a violation for total trihalomethanes (TTHM) at this utility in 2023. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 64.7 ppb, in 2016, and EPA recorded a violation in 2017.

What handles it

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

Above the health goal1

Arsenic

Comes from the source

Above the health goal

4.5ppb

Highest yearly average, 2020 to 2026

2026 average: 3.7 ppb

Averaged by year, the highest was 4.5 ppb, in 2020: below EPA’s legal limit of 10 ppb, but above its health goal of zero. Its highest single sample was 5.9 ppb. In 2026, the latest year on file, its 10 samples averaged 3.7 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 4.4 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”

Below EPA’s limits3

Haloacetic acids (HAA5)

Forms or is added in treatment

Below EPA’s limits

45ppb

Highest yearly average, 2020 to 2026

2026 average: 9.1 ppb

Averaged by year, the highest was 45 ppb, in 2023, below EPA’s legal limit of 60 ppb. Its highest single sample was 110 ppb. In 2026, the latest year on file, its two samples averaged 9.1 ppb. EPA recorded no violation for haloacetic acids (HAA5) at this utility since 2020. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 47.5 ppb, in 2019.

What handles it

No certification claim covers this compound yet.

Nitrate

Comes from the source

Below EPA’s limits

1.8ppm

Highest sample; found in 4 of 24

2026: not found

The highest sample, in 2022, was 1.8 ppm, below EPA’s legal limit of 10 ppm. In 2026, the latest year on file, it wasn’t found in any of its three samples. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 2.5 ppm, in 2014.

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

0.4ppm

Highest yearly average, 2022 to 2025

2025 average: 0.25 ppm

Averaged by year, the highest was 0.4 ppm, in 2022, below EPA’s legal limit of 4.0 ppm. Its highest single sample was 0.44 ppm. In 2025, the latest year on file, its three samples averaged 0.25 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.33 ppm, in 2018.

What handles it

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

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

    For: Copper, Total trihalomethanes (TTHM), Arsenic

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

  • NSF/ANSI 58

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

    For: Copper, Total trihalomethanes (TTHM), 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 550 mg/L (32.2 grains per gallon), across 3 sampling points, 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 32.2 grains per gallon, salt includedSoftener or salt-free conditioner?California water hardness, utility by utility

Violations since 2016

Contaminant or ruleTypePeriodMeasuredStatus
TTHMThe running average was above the legal limit.EPA: Maximum Contaminant Level Violation, AverageOct. 1, 2023 to Dec. 31, 20230.081 MG/LResolved
TTHMThe running average was above the legal limit.EPA: Maximum Contaminant Level Violation, AverageJan. 1, 2017 to March 31, 20170.081 MG/LResolved
Health-based violations only. Resolved and archived mean the utility returned to compliance or the state closed the record.

What this report can’t tell you

  • Everything else. Total trihalomethanes (TTHM), arsenic, haloacetic acids (HAA5), nitrate, fluoride and chromium (total) results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. San Miguelito MWC’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. 13, 2020 to May 6, 2026.

Testing your own tap

San Miguelito MWC’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 San Miguelito MWC serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.

  • Abalone Coast Analytical, Inc.

    San Luis Obispo, CA · about 5 miles

    Certified for bacteria

    (805) 595-1080

  • Fruit Growers Laboratory, Inc.

    San Luis Obispo, CA · about 6 miles

    Certified for bacteria

    (805) 783-2940

  • County of San Luis Obispo Public Health Laboratory

    San Luis Obispo, CA · about 8 miles

    Certified for bacteria

    (805) 781-5507

All 145 certified labs for California

Sources

PWSID CA4010003. Rebuilt from EPA data on Oct. 18, 2026.

Towns it serves

Also in San Luis Obispo County

All California utilities

What to do next