Mustang Springs 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
- 30 people
- Connections
- 16
- Water source
- Groundwater
- Based in
- Paso Robles, CA
- County
- San Luis Obispo
- Owner
- Private
- Hardness
- Very hard
The ZIP code it serves
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. 3 health-based violations since 2016.
What was found
Fluoride, nitrate, total trihalomethanes (TTHM), arsenic, chromium (total) and haloacetic acids (HAA5): California’s own results, samples taken from Jan. 2, 2020 to July 1, 2026, with EPA’s 2012 to 2019 file for earlier years.
Below EPA’s limits3
Fluoride
Forms or is added in treatment
3.1ppm
Highest yearly average, 2020 to 2026
2026 average: 1.6 ppm
Averaged by year, the highest was 3.1 ppm, in 2020, below EPA’s legal limit of 4.0 ppm. Its highest single sample was 10 ppm. In 2026, the latest year on file, its eight samples averaged 1.6 ppm. EPA recorded no violation for fluoride at this utility since 2020. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 3.2 ppm, in 2018.
What handles it
- NSF/ANSI 58 look for “Fluoride Reduction”
- NSF/ANSI 53 look for “Fluoride”
Nitrate
Comes from the source
1.0ppm
Highest sample; found in 4 of 9
2026, one sample: 0.62 ppm
The highest sample, in 2022, was 1.0 ppm, below EPA’s legal limit of 10 ppm. In 2026, the latest year on file, its one sample was 0.62 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 0.7 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
3.7ppb
Highest yearly average, 2022 to 2023
Averaged by year, the highest was 3.7 ppb, in 2023, below EPA’s legal limit of 80 ppb. That was also the latest year on file.
What handles it
- NSF/ANSI 53 look for “Trihalomethanes (TTHM) Reduction”
- NSF/ANSI 58 look for “Trihalomethanes (TTHM) Reduction”
4 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
- Arsenic
- Chromium (total)
- Haloacetic acids (HAA5)
- Lead
Hardness
Very hard, typically 324 mg/L (19 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.
Violations since 2016
| Contaminant or rule | Type | Period | Measured | Status |
|---|---|---|---|---|
| Fluoride | A sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single Sample | Oct. 1, 2022 to Dec. 31, 2022 | 0.9 MG/L | Resolved |
| Fluoride | A sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single Sample | July 1, 2022 to Sept. 30, 2022 | 1.7 MG/L | Resolved |
| Fluoride | A sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single Sample | July 1, 2016 to Oct. 1, 2016 | 2.8 MG/L | Resolved |
| 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. Fluoride, nitrate, total trihalomethanes (TTHM), arsenic, chromium (total) and haloacetic acids (HAA5) results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Mustang Springs 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 Jan. 2, 2020 to July 1, 2026.
Testing your own tap
The 3 labs California certifies closest to the area Mustang Springs 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 27 miles
Certified for bacteria
Fruit Growers Laboratory, Inc.
San Luis Obispo, CA · about 29 miles
Certified for bacteria
Abalone Coast Analytical, Inc.
San Luis Obispo, CA · about 29 miles
Certified for bacteria
Sources
- EPA UCMR 5 occurrence data, file of Oct. 15, 2026
- EPA SDWA bulk download (SDWIS federal data), 2026 Q3
- California State Water Resources Control Board, Division of Drinking Water, results from Jan. 1, 2020 to July 17, 2026, read Oct. 8, 2026
- EPA Six-Year Review 4 compliance monitoring data, 2012 to 2019, file of Feb. 5, 2024
- Certified labs: California State Water Resources Control Board, ELAP accredited laboratories and their fields of accreditation, read Oct. 17, 2026; distances from the Census 2020 ZIP code tabulation area gazetteer
- Hardness: California State Water Resources Control Board, Division of Drinking Water, results from Jan. 5, 2021 to March 5, 2024, read Oct. 10, 2026
- Limits and goals: each contaminant’s page, with its EPA source.
- How this page is built: methodology.
PWSID CA4000775. Rebuilt from EPA data on Oct. 18, 2026.
What to do next
- Nothing here is above a health goalIn EPA’s and California’s records for this utility. They don’t cover everything, which is why the next step matters.Every contaminant TapBuff tracks
- Get the utility’s own reportMustang Springs Mutual Water must send you a water quality report every year. It covers contaminants this page does not show.How to read it
- Test your own tap for leadYour service line, solder and fixtures decide the lead at your faucet, not the utility’s average.Lead in your water: what to do
- Decide if you want a filter at allA filter for taste or chlorine is a preference, not a need. The standards say what each kind can do.NSF/ANSI standards, decoded