Union Heights 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
- 98 people
- Connections
- 29
- Water source
- Groundwater
- Based in
- Hollister, CA
- County
- San Benito
- 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. No health-based violations on file since 2016.
What was found
Nitrate, haloacetic acids (HAA5), arsenic, chromium (total), fluoride, total trihalomethanes (TTHM) and uranium: California’s own results, samples taken from May 4, 2020 to May 12, 2026, with EPA’s 2012 to 2019 file for earlier years.
Below EPA’s limits2
Nitrate
Comes from the source
3.5ppm
Highest sample; found in 2 of 11
2026: not found
The highest sample, in 2020, was 3.5 ppm, below EPA’s legal limit of 10 ppm. In 2026, the latest year on file, it wasn’t found in its one sample. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 1.5 ppm, in 2012.
What handles it
- NSF/ANSI 58 look for “Nitrate/Nitrite Reduction”
- NSF/ANSI 53 look for “Nitrate/Nitrite (30 ppm challenge)”
Haloacetic acids (HAA5)
Forms or is added in treatment
2.9ppb
Highest yearly average, 2021 to 2024
Averaged by year, the highest was 2.9 ppb, in 2024, below EPA’s legal limit of 60 ppb. That was also the latest year on file.
What handles it
No certification claim covers this compound yet.
6 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
- Arsenic
- Chromium (total)
- Fluoride
- Lead
- Total trihalomethanes (TTHM)
- Uranium
Hardness
Very hard, 280 mg/L (16.4 grains per gallon), at its one sampling point, 2020 to 2023.
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
No health-based violations on file with EPA since 2016.
What this report can’t tell you
Everything else. Nitrate, haloacetic acids (HAA5), arsenic, chromium (total), fluoride, total trihalomethanes (TTHM) and uranium results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Union Heights 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 May 4, 2020 to May 12, 2026.
Testing your own tap
The 3 labs California certifies closest to the area Union Heights MWC serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.
CM Analytical, Inc.
Gilroy, CA · about 13 miles
Certified for bacteria
Monterey County Consolidated Environmental Laboratory
Salinas, CA · about 21 miles
Certified for bacteria, nitrate, lead and copper, metals, minerals and other inorganics
Bracewell Engineering, Inc.
Morgan Hill, CA · about 22 miles
Certified for bacteria, nitrate, minerals and other inorganics
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 Nov. 17, 2020 to Nov. 14, 2023, read Oct. 10, 2026
- Limits and goals: each contaminant’s page, with its EPA source.
- How this page is built: methodology.
PWSID CA3500825. 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 reportUnion Heights MWC 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