Twin Valley Inc
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
- 317 people
- Connections
- 96
- Water source
- Groundwater
- Based in
- Castroville, CA
- County
- Santa Clara
- Owner
- Private
- Hardness
- Varies by source
The ZIP code it serves
The short answer
1 result is above EPA’s legal limit, and 1 more is above the health goal. The worst: Nitrate, above the legal limit. 54 health-based violations since 2016.
What handles itWhat was found
Lead and copper: EPA SDWIS monitoring periods ending 2009 to 2025.
Nitrate, total trihalomethanes (TTHM), chromium (total), fluoride, arsenic and haloacetic acids (HAA5): California’s own results, samples taken from Jan. 13, 2020 to June 1, 2026, with EPA’s 2012 to 2019 file for earlier years.
Above the legal limit1
Nitrate
Comes from the source
12.1ppm
Highest sample; found in 96 of 98
2026 average: 8.3 ppm
From 2020 to 2025, at least 25 samples were above EPA’s legal limit of 10 ppm, the highest 12.1 ppm in 2020. The next sample at the same point, within 30 days, kept the average above the limit for 15; 10 have no follow-up sample on file within 30 days. In 2026, the latest year on file, its eight samples averaged 8.3 ppm. EPA recorded violations for nitrate at this utility in 2020, 2021, 2022 and 2023. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 12.4 ppm, in 2016, and EPA recorded violations in 2017, 2018 and 2019.
What handles it
- NSF/ANSI 58 look for “Nitrate/Nitrite Reduction”
- NSF/ANSI 53 look for “Nitrate/Nitrite (30 ppm challenge)”
Above the health goal1
Lead
Comes from pipes, often your own
3.9ppb
90th percentile, 2023 to 2025
In the latest period, 9 in 10 homes sampled were at or below 3.9 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
- NSF/ANSI 53 look for “Lead Reduction”
- NSF/ANSI 58 look for “Lead Reduction”
Below EPA’s limits3
Total trihalomethanes (TTHM)
Forms or is added in treatment
5.0ppb
Highest yearly average, 2020 to 2025
2025: not found
Averaged by year, the highest was 5.0 ppb, in 2020, below EPA’s legal limit of 80 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 2.0 ppb, in 2019.
What handles it
- NSF/ANSI 53 look for “Trihalomethanes (TTHM) Reduction”
- NSF/ANSI 58 look for “Trihalomethanes (TTHM) Reduction”
Chromium (total)
Comes from the source
3.0ppb
Highest yearly average, 2021 to 2026
2026: not found
Averaged by year, the highest was 3.0 ppb, in 2022, below EPA’s legal limit of 100 ppb. Its highest single sample was 3.7 ppb. 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 yearly average of 3.7 ppb, in 2018.
What handles it
- NSF/ANSI 58 look for “Chromium (Hexavalent) Reduction”
- NSF/ANSI 53 look for “Chromium Reduction”
Fluoride
Forms or is added in treatment
0.1ppm
Highest yearly average, 2021 to 2026
2026, one sample: 0.1 ppm
Averaged by year, the highest was 0.1 ppm, in 2021, below EPA’s legal limit of 4.0 ppm. In 2026, the latest year on file, its one sample was 0.1 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.2 ppm, in 2014.
What handles it
- NSF/ANSI 58 look for “Fluoride Reduction”
- NSF/ANSI 53 look for “Fluoride”
2 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
- Arsenic
- Haloacetic acids (HAA5)
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: Nitrate/Nitrite (30 ppm challenge), Lead Reduction
For: Nitrate, Lead
- NSF/ANSI 58
Claims: Nitrate/Nitrite Reduction, Lead Reduction
For: Nitrate, Lead
Other certifiers’ wording: Nitrate
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
Countertop reverse osmosis
- IAPMO listing:NSF/ANSI 42NSF/ANSI 53NSF/ANSI 58NSF/ANSI 401checked Oct. 4, 2026
Certified for: Nitrate, Lead
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, Lead
Culligan 10-Cup Pitcher with ZeroWater Technology (ZEROP10)
Pitcher
- IAPMO listing:NSF/ANSI 42NSF/ANSI 53NSF/ANSI 401checked Oct. 9, 2026
Certified for: Nitrate, Lead
Brita Tahoe Pitcher with Elite Filter (OB60, OB06)
Pitcher
- WQA listing:NSF/ANSI 42NSF/ANSI 53NSF/ANSI 401checked Oct. 13, 2026
- IAPMO listing:NSF/ANSI 53checked Oct. 13, 2026
Certified for: Lead
Brita Everyday Pitcher with Elite Filter (OB46, OB06)
Pitcher
- WQA listing:NSF/ANSI 42NSF/ANSI 53NSF/ANSI 401checked Oct. 13, 2026
Certified for: Lead
Hardness
Soft to very hard depending on the source, 12 to 272 mg/L (0.7 to 15.9 grains per gallon), across 4 sampling points, 2021 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.
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 | Nov. 1, 2023 to Nov. 30, 2023 | 10.5 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, 2023 to July 31, 2023 | 10.6 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 | June 1, 2023 to June 30, 2023 | 10.5 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 | Nov. 1, 2022 to Nov. 30, 2022 | 10.6 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, 2022 to Oct. 31, 2022 | 10.7 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 | Sept. 1, 2022 to Sept. 30, 2022 | 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 | Aug. 1, 2022 to Aug. 31, 2022 | 10.7 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, 2022 to July 31, 2022 | 10.8 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 | May 1, 2022 to May 31, 2022 | 10.5 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 | Dec. 1, 2021 to Dec. 31, 2021 | 10.8 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 | Nov. 1, 2021 to Nov. 30, 2021 | 11.1 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, 2021 to Oct. 31, 2021 | 10.8 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 | Sept. 1, 2021 to Sept. 30, 2021 | 11.3 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 | Aug. 1, 2021 to Aug. 31, 2021 | 11.3 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, 2021 to July 31, 2021 | 11.4 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 | June 1, 2021 to June 30, 2021 | 11.6 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 | May 1, 2021 to May 31, 2021 | 11.5 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, 2021 to April 30, 2021 | 11.6 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 | March 1, 2021 to March 31, 2021 | 11.4 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 | Feb. 1, 2021 to Feb. 28, 2021 | 11.7 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, 2021 to Jan. 31, 2021 | 11.9 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 | Dec. 1, 2020 to Dec. 31, 2020 | 12.1 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 | Nov. 1, 2020 to Nov. 30, 2020 | 11.8 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, 2020 to Oct. 31, 2020 | 11.5 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 | Aug. 1, 2020 to Aug. 31, 2020 | 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, 2020 to July 31, 2020 | 11.8 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 | June 1, 2020 to June 30, 2020 | 11.7 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 | May 1, 2020 to May 31, 2020 | 11.5 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, 2020 to April 30, 2020 | 10.5 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 | March 1, 2020 to March 31, 2020 | 11.7 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 | Feb. 1, 2020 to Feb. 29, 2020 | 11.6 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, 2020 to Jan. 31, 2020 | 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 | Dec. 1, 2019 to Dec. 31, 2019 | 11.5 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 | Nov. 1, 2019 to Nov. 30, 2019 | 11.9 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, 2019 to Oct. 31, 2019 | 11.8 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 | Sept. 1, 2019 to Sept. 30, 2019 | 11.3 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 | Aug. 1, 2019 to Aug. 31, 2019 | 11.5 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, 2019 to July 31, 2019 | 11.9 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 | June 1, 2019 to June 30, 2019 | 11.1 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 | May 1, 2019 to May 31, 2019 | 11.5 MG/L | Archived |
| Health-based violations only. Resolved and archived mean the utility returned to compliance or the state closed the record. 8 monitoring or reporting violations not shown. | ||||
What this report can’t tell you
Everything else. Nitrate, total trihalomethanes (TTHM), chromium (total), fluoride, arsenic and haloacetic acids (HAA5) results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Twin Valley Inc’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 June 1, 2026.
Testing your own tap
The 3 labs California certifies closest to the area Twin Valley Inc serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.
Bracewell Engineering, Inc.
Morgan Hill, CA · about 4 miles
Certified for bacteria, nitrate, minerals and other inorganics
CM Analytical, Inc.
Gilroy, CA · about 12 miles
Certified for bacteria
Torrent Laboratory, Inc
Milpitas, CA · about 23 miles
Certified for bacteria, nitrate, lead and copper, metals, minerals and other inorganics, organic chemicals, disinfection byproducts, PFAS
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. 8, 2021 to Jan. 7, 2026, read Oct. 10, 2026
- Limits and goals: each contaminant’s page, with its EPA source.
- How this page is built: methodology.
PWSID CA4300575. Rebuilt from EPA data on Oct. 18, 2026.
What to do next
- Read up on the 2 results above a lineWhat each one does to health, where it comes from, and the certification claim that addresses it.Start with Nitrate
- Get the utility’s own reportTwin Valley Inc 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
- Compare certified filtersWhat the filters certified for these results cost over five years, cartridges included.Compare five-year costs