Woodland Park Mutual Water Co
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
- 538 people
- Connections
- 163
- Water source
- Groundwater
- Based in
- Arroyo Grande, CA
- County
- San Luis Obispo
- Owner
- Private
- Hardness
- Varies by source
The ZIP code it serves
The short answer
1 result is above EPA’s legal limit. The worst: Nitrate, above the legal limit. 13 health-based violations since 2016.
What handles itWhat was found
Nitrate, total trihalomethanes (TTHM), haloacetic acids (HAA5), arsenic, chromium (total) and fluoride: California’s own results, samples taken from Jan. 15, 2020 to July 1, 2026, with EPA’s 2012 to 2019 file for earlier years.
Uranium: EPA’s compliance monitoring file, samples taken from Dec. 3, 2018 to Dec. 3, 2018. Newer results are in the utility’s annual water quality report.
Above the legal limit1
Nitrate
Comes from the source
22ppm
Highest sample; found in 78 of 78
2026 average: 13.1 ppm
From 2020 to 2026, at least 25 samples were above EPA’s legal limit of 10 ppm, the highest 22 ppm in 2026. The next sample at the same point, within 30 days, kept the average above the limit for two; one came back under and 22 have no follow-up sample on file within 30 days. That was also the latest year on file, and its 10 samples averaged 13.1 ppm, above the limit. EPA recorded violations for nitrate at this utility in 2023, 2024, 2025 and 2026. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 17.8 ppm, in 2019.
What handles it
- NSF/ANSI 58 look for “Nitrate/Nitrite Reduction”
- NSF/ANSI 53 look for “Nitrate/Nitrite (30 ppm challenge)”
Below EPA’s limits2
Total trihalomethanes (TTHM)
Forms or is added in treatment
11ppb
Highest yearly average, 2023
Averaged by year, the highest was 11 ppb, in 2023, below EPA’s legal limit of 80 ppb. That is the only year on file. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 8.1 ppb, in 2019.
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
2.1ppb
Highest yearly average, 2023
Averaged by year, the highest was 2.1 ppb, in 2023, below EPA’s legal limit of 60 ppb. That is the only year on file.
What handles it
No certification claim covers this compound yet.
5 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
- Arsenic
- Chromium (total)
- Fluoride
- Lead
- 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
Claim: Nitrate/Nitrite (30 ppm challenge)
For: Nitrate
- NSF/ANSI 58
Claim: Nitrate/Nitrite Reduction
For: Nitrate
Other certifiers’ wording: Nitrate
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
Countertop reverse osmosis
- IAPMO listing:NSF/ANSI 42NSF/ANSI 53NSF/ANSI 58NSF/ANSI 401checked Oct. 4, 2026
Certified for: Nitrate
Aquasana SmartFlow Reverse Osmosis (AQ-SFRO2)
Under-sink reverse osmosis
- WQA listing:NSF/ANSI 42NSF/ANSI 53NSF/ANSI 58NSF/ANSI 401checked Oct. 9, 2026
Certified for: Nitrate
Culligan 10-Cup Pitcher with ZeroWater Technology (ZEROP10)
Pitcher
- IAPMO listing:NSF/ANSI 42NSF/ANSI 53NSF/ANSI 401checked Oct. 9, 2026
Certified for: Nitrate
Hardness
Hard to very hard depending on the source, 170 to 190 mg/L (9.9 to 11.1 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 |
|---|---|---|---|---|
| Nitrate | A sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single Sample | April 1, 2026 to June 30, 2026 | 22 MG/L | Archived |
| Nitrate | A sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single Sample | Jan. 1, 2026 to March 31, 2026 | 12 MG/L | Archived |
| Nitrate | 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, 2025 to Dec. 31, 2025 | 12 MG/L | Archived |
| Nitrate | 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, 2025 to Sept. 30, 2025 | 11 MG/L | Archived |
| Nitrate | A sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single Sample | April 1, 2025 to June 30, 2025 | 12 MG/L | Archived |
| Nitrate | A sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single Sample | Jan. 1, 2025 to March 31, 2025 | 19 MG/L | Archived |
| Nitrate | 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, 2024 to Dec. 31, 2024 | 19 MG/L | Archived |
| Nitrate | 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, 2024 to Sept. 30, 2024 | 11 MG/L | Archived |
| Nitrate | A sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single Sample | April 1, 2024 to June 30, 2024 | 11 MG/L | Archived |
| Nitrate | A sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single Sample | Jan. 1, 2024 to March 31, 2024 | 11 MG/L | Archived |
| Nitrate | 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, 2023 to Dec. 31, 2023 | 11 MG/L | Archived |
| Nitrate | A sample was above the legal limit, for a contaminant judged one sample at a time.EPA: Maximum Contaminant Level Violation, Single Sample | April 1, 2023 to June 30, 2023 | 11 MG/L | Archived |
| Nitrate | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | April 1, 2023 to June 30, 2023 | 11 MG/L | Archived |
| Health-based violations only. Resolved and archived mean the utility returned to compliance or the state closed the record. 3 monitoring or reporting violations not shown. | ||||
What this report can’t tell you
Everything else. Nitrate, total trihalomethanes (TTHM), haloacetic acids (HAA5), arsenic, chromium (total) and fluoride results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Uranium comes from EPA’s file alone, which ends in 2019. Woodland Park Mutual Water Co’s own annual report, which it must send you every year, has newer results for those and 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. 15, 2020 to July 1, 2026; EPA’s compliance samples are from Dec. 3, 2018 to Dec. 3, 2018.
Testing your own tap
The 3 labs California certifies closest to the area Woodland Park Mutual Water Co 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 12 miles
Certified for bacteria
Fruit Growers Laboratory, Inc.
San Luis Obispo, CA · about 12 miles
Certified for bacteria
Abalone Coast Analytical, Inc.
San Luis Obispo, CA · about 12 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 Sept. 22, 2021 to Nov. 4, 2024, read Oct. 10, 2026
- Limits and goals: each contaminant’s page, with its EPA source.
- How this page is built: methodology.
PWSID CA4000506. Rebuilt from EPA data on Oct. 18, 2026.
What to do next
- Read up on NitrateWhat each one does to health, where it comes from, and the certification claim that addresses it.About Nitrate
- Get the utility’s own reportWoodland Park Mutual Water Co must send you a water quality report every year. It covers contaminants this page does not show, and has newer results than EPA’s national file for the ones here that come from it.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
- Compare certified filtersWhat the filters certified for these results cost over five years, cartridges included.Compare five-year costs