Twin Lakes Resort
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
- 400 people
- Connections
- 153
- Water source
- Groundwater
- Based in
- La Mesa, CA
- County
- San Diego
- Owner
- Private
- Hardness
- Varies by source
The ZIP code it serves
The short answer
1 result is above EPA’s legal limit, and 2 more are above the health goal. The worst: Arsenic, above the legal limit. 35 health-based violations since 2016.
What handles itWhat was found
Arsenic, nitrate, uranium, total trihalomethanes (TTHM), fluoride and chromium (total): California’s own results, samples taken from Jan. 29, 2020 to June 23, 2026, with EPA’s 2012 to 2019 file for earlier years.
Above the legal limit1
Arsenic
Comes from the source
12ppb
Highest yearly average, 2020 to 2026
2026: not found
Averaged by year, the highest was 12 ppb, in 2023, above EPA’s legal limit of 10 ppb. Its highest single sample was 13 ppb. In 2026, the latest year on file, it wasn’t found in any of its two samples. EPA recorded violations for arsenic at this utility in 2020, 2021, 2022, 2023, 2024 and 2025. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 12 ppb, in 2017, and EPA recorded violations in 2016, 2017, 2018 and 2019.
What handles it
- NSF/ANSI 58 look for “Arsenic (Pentavalent)<=50 ppb Reduction”
- NSF/ANSI 53 look for “Arsenic (Pentavalent)<=50 ppb Reduction”
Above the health goal2
Nitrate
Comes from the source
11ppm
Highest sample; found in 6 of 6
2025, one sample: 1.6 ppm
One sample, in 2021, was above EPA’s legal limit of 10 ppm, at 11 ppm. No follow-up sample at that point within 30 days is on file. 10 ppm is also EPA’s health goal. In 2025, the latest year on file, its one sample was 1.6 ppm. EPA recorded no violation for nitrate at this utility since 2020. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 1.4 ppm, in 2018.
What handles it
- NSF/ANSI 58 look for “Nitrate/Nitrite Reduction”
- NSF/ANSI 53 look for “Nitrate/Nitrite (30 ppm challenge)”
Uranium
Comes from the source
29.7ppb
Highest yearly average, 2021 to 2026
2026 average: 25.3 ppb
Averaged by year, the highest was 29.7 ppb, in 2022: below EPA’s legal limit of 30 ppb, but above its health goal of zero. In 2026, the latest year on file, its two samples averaged 25.3 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 35.2 ppb, in 2018.
What handles it
- NSF/ANSI 58 look for “Uranium”
Below EPA’s limits2
Total trihalomethanes (TTHM)
Forms or is added in treatment
8.4ppb
Highest yearly average, 2021 to 2025
2025: not found
Averaged by year, the highest was 8.4 ppb, in 2021, below EPA’s legal limit of 80 ppb. Its highest single sample was 12 ppb. In 2025, the latest year on file, it wasn’t found in its one sample.
What handles it
- NSF/ANSI 53 look for “Trihalomethanes (TTHM) Reduction”
- NSF/ANSI 58 look for “Trihalomethanes (TTHM) Reduction”
Fluoride
Forms or is added in treatment
0.2ppm
Highest yearly average, 2021 to 2025
2025, one sample: 0.2 ppm
Averaged by year, the highest was 0.2 ppm, in 2021, below EPA’s legal limit of 4.0 ppm. Its highest single sample was 0.3 ppm. In 2025, the latest year on file, its one sample was 0.2 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.4 ppm, in 2018.
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.
- Chromium (total)
- Lead
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, Nitrate/Nitrite (30 ppm challenge)
For: Arsenic, Nitrate
Other certifiers’ wording: Arsenic (III) (50 ppb influent level)
- NSF/ANSI 58
Claims: Arsenic (Pentavalent)<=50 ppb Reduction, Nitrate/Nitrite Reduction, Uranium
For: Arsenic, Nitrate, Uranium
Other certifiers’ wording: Arsenic (Pentavalent)<=300 ppb Reduction; Arsenic (V) (300 ppb influent level); 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: Arsenic, 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: Arsenic, Nitrate
Brondell Capella RC250 Reverse Osmosis System
Under-sink reverse osmosis
- WQA listing:NSF/ANSI 42NSF/ANSI 53NSF/ANSI 58NSF/ANSI 401checked Oct. 9, 2026
Certified for: Arsenic
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
Soft to hard depending on the source, 16 to 180 mg/L (0.9 to 10.5 grains per gallon), across 3 sampling points, 2021 to 2025.
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 |
|---|---|---|---|---|
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | April 1, 2025 to June 30, 2025 | 11.7 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Jan. 1, 2025 to March 31, 2025 | 12 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Oct. 1, 2024 to Dec. 31, 2024 | 11.7 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | July 1, 2024 to Sept. 30, 2024 | 11.7 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | April 1, 2024 to June 30, 2024 | 12 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Jan. 1, 2024 to March 31, 2024 | 12 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Oct. 1, 2023 to Dec. 31, 2023 | 12 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | July 1, 2023 to Sept. 30, 2023 | 12 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | April 1, 2023 to June 30, 2023 | 12.2 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Jan. 1, 2023 to March 31, 2023 | 12.1 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Oct. 1, 2022 to Dec. 31, 2022 | 11.9 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | July 1, 2022 to Sept. 30, 2022 | 11.6 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | April 1, 2022 to June 30, 2022 | 11.6 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Jan. 1, 2022 to March 31, 2022 | 11.5 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | July 1, 2021 to Sept. 30, 2021 | 11.5 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | April 1, 2021 to June 30, 2021 | 11.2 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Jan. 1, 2021 to March 31, 2021 | 11.3 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Oct. 1, 2020 to Dec. 31, 2020 | 11.1 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | July 1, 2020 to Sept. 30, 2020 | 11.6 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | April 1, 2020 to June 30, 2020 | 11.7 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Jan. 1, 2020 to March 31, 2020 | 11.2 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Oct. 1, 2019 to Dec. 31, 2019 | 11.1 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | July 1, 2019 to Sept. 30, 2019 | 11 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | April 1, 2019 to June 30, 2019 | 11 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Jan. 1, 2019 to March 31, 2019 | 11.2 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Oct. 1, 2018 to Dec. 31, 2018 | 11.3 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | April 1, 2018 to June 30, 2018 | 12 MG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Jan. 1, 2018 to March 31, 2018 | 12 MG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Oct. 1, 2017 to Dec. 31, 2017 | 12 MG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | July 1, 2017 to Sept. 30, 2017 | 11.8 UG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | April 1, 2017 to June 30, 2017 | 0.012 MG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Jan. 1, 2017 to March 31, 2017 | 0.011 MG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | Oct. 1, 2016 to Dec. 31, 2016 | 0.011 MG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | July 1, 2016 to Sept. 30, 2016 | 0.011 MG/L | Archived |
| Arsenic | The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, Average | April 1, 2016 to June 30, 2016 | 0.012 MG/L | Archived |
| Health-based violations only. Resolved and archived mean the utility returned to compliance or the state closed the record. 22 monitoring or reporting violations not shown. | ||||
What this report can’t tell you
Everything else. Arsenic, nitrate, uranium, total trihalomethanes (TTHM), fluoride and chromium (total) results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Twin Lakes Resort’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. 29, 2020 to June 23, 2026.
Testing your own tap
The 3 labs California certifies closest to the area Twin Lakes Resort serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.
Metropolitan Solutions
National City, CA · about 29 miles
Certified for bacteria
Environmental Laboratory Network, Inc.
San Diego, CA · about 31 miles
Certified for bacteria, nitrate, lead and copper, metals, minerals and other inorganics, radioactivity
Analytical Environmental Lab, LLC
San Diego, CA · about 34 miles
Certified for bacteria, nitrate, lead and copper, metals, minerals and other inorganics, disinfection byproducts
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 Oct. 19, 2021 to March 24, 2025, read Oct. 10, 2026
- Limits and goals: each contaminant’s page, with its EPA source.
- How this page is built: methodology.
PWSID CA3701793. Rebuilt from EPA data on Oct. 18, 2026.
What to do next
- Read up on the 3 results above a lineWhat each one does to health, where it comes from, and the certification claim that addresses it.Start with Arsenic
- Get the utility’s own reportTwin Lakes Resort 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