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Slo Cwwd No. 23 - Santa Margarita

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
1,291 people
Connections
505
Water source
Groundwater
Based in
San Luis Obispo, CA
County
San Luis Obispo
Owner
Local government
Hardness
Varies by source
The ZIP code it serves

93453

The short answer

2 results are above the health goal. The worst: Arsenic, above the health goal. No health-based violations on file since 2016.

What handles it

What was found

Lead and copper: EPA SDWIS monitoring periods ending 2007 to 2026.

Copper: EPA’s file records a utility’s copper only when it exceeds the action level. The last here was 1.8 ppm, for the period ending Dec. 31, 1993. None since is on file, so it is not counted as a current finding.

Arsenic, nitrate, total trihalomethanes (TTHM), haloacetic acids (HAA5), fluoride, chromium (total) and uranium: California’s own results, samples taken from Jan. 6, 2020 to June 1, 2026, with EPA’s 2012 to 2019 file for earlier years.

Above the health goal2

Arsenic

Comes from the source

Above the health goal

3.0ppb

Highest yearly average, 2020 to 2026

2026 average: 2.8 ppb

Averaged by year, the highest was 3.0 ppb, in 2021: below EPA’s legal limit of 10 ppb, but above its health goal of zero. Its highest single sample was 6.0 ppb. In 2026, the latest year on file, its 20 samples averaged 2.8 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 5.1 ppb, in 2017.

What handles it

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

Lead

Comes from pipes, often your own

Above the health goal

1.4ppb

90th percentile, 2024 to 2026

In the latest period, 9 in 10 homes sampled were at or below 1.4 ppb, below EPA’s action level of 15 ppb. The action level drops to 10 ppb on Nov. 1, 2027. EPA’s health goal for lead is zero.

What handles it

Below EPA’s limits5

Nitrate

Comes from the source

Below EPA’s limits

7.0ppm

Highest sample; found in 31 of 50

2026 average: 0.49 ppm

The highest sample, in 2023, was 7.0 ppm, below EPA’s legal limit of 10 ppm. In 2026, the latest year on file, its nine samples averaged 0.49 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 4.5 ppm, in 2017.

What handles it

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

Total trihalomethanes (TTHM)

Forms or is added in treatment

Below EPA’s limits

16ppb

Highest yearly average, 2020 to 2025

2025 average: 0.5 ppb

Averaged by year, the highest was 16 ppb, in 2023, below EPA’s legal limit of 80 ppb. In 2025, the latest year on file, its two samples averaged 0.5 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 13.6 ppb, in 2015.

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

5.5ppb

Highest yearly average, 2020 to 2025

2025: not found

Averaged by year, the highest was 5.5 ppb, in 2020, below EPA’s legal limit of 60 ppb. In 2025, the latest year on file, it wasn’t found in its one sample. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 3.9 ppb, in 2019.

What handles it

No certification claim covers this compound yet.

Fluoride

Forms or is added in treatment

Below EPA’s limits

0.12ppm

Highest yearly average, 2020 to 2026

Averaged by year, the highest was 0.12 ppm, in 2026, below EPA’s legal limit of 4.0 ppm. Its highest single sample was 0.14 ppm. That was also the latest year on file. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.19 ppm, in 2017.

What handles it

Chromium (total)

Comes from the source

Below EPA’s limits

0.45ppb

Highest yearly average, 2020 to 2026

Averaged by year, the highest was 0.45 ppb, in 2026, below EPA’s legal limit of 100 ppb. Its highest single sample was 0.92 ppb. That was also the latest year on file.

What handles it

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

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

    For: Arsenic, Lead

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

  • NSF/ANSI 58

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

    For: Arsenic, Lead

    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

The best water filters for lead, ranked

Hardness

Hard to very hard depending on the source, 151 to 282 mg/L (8.8 to 16.5 grains per gallon), across 5 sampling points, 2019 to 2026.

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. Arsenic, nitrate, total trihalomethanes (TTHM), haloacetic acids (HAA5), fluoride, chromium (total) and uranium results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Slo Cwwd No. 23 - Santa Margarita’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. 6, 2020 to June 1, 2026.

Testing your own tap

Slo Cwwd No. 23 - Santa Margarita’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 Slo Cwwd No. 23 - Santa Margarita 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 22 miles

    Certified for bacteria

    (805) 781-5507

  • Fruit Growers Laboratory, Inc.

    San Luis Obispo, CA · about 23 miles

    Certified for bacteria

    (805) 783-2940

  • Abalone Coast Analytical, Inc.

    San Luis Obispo, CA · about 24 miles

    Certified for bacteria

    (805) 595-1080

All 145 certified labs for California

Sources

PWSID CA4010024. Rebuilt from EPA data on Oct. 18, 2026.

Also in San Luis Obispo County

All California utilities

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