Los Angeles Cwwd 40, Reg. 39 - Rock Creek
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
- 1,030 people
- Connections
- 368
- Water source
- Surface water bought from another system
- Based in
- Alhambra, CA
- County
- Los Angeles
- Owner
- Local government
- Hardness
- Very hard
The ZIP code it serves
The short answer
1 result is above the health goal. The worst: Uranium, above the health goal. No health-based violations on file since 2016.
What handles itWhat was found
Uranium, total trihalomethanes (TTHM), haloacetic acids (HAA5), fluoride, nitrate, arsenic and chromium (total): California’s own results, samples taken from Feb. 24, 2020 to May 20, 2026, with EPA’s 2012 to 2019 file for earlier years.
Above the health goal1
Uranium
Comes from the source
4.6ppb
Highest yearly average, 2022 to 2023
2023, one sample: 2.8 ppb
Averaged by year, the highest was 4.6 ppb, in 2022: below EPA’s legal limit of 30 ppb, but above its health goal of zero. In 2023, the latest year on file, its one sample was 2.8 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 1.8 ppb, in 2015.
What handles it
- NSF/ANSI 58 look for “Uranium”
Below EPA’s limits4
Total trihalomethanes (TTHM)
Forms or is added in treatment
24ppb
Highest yearly average, 2021 to 2026
2026 average: 19 ppb
Averaged by year, the highest was 24 ppb, in 2023, below EPA’s legal limit of 80 ppb. Its highest single sample was 67 ppb. In 2026, the latest year on file, its four samples averaged 19 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 22.5 ppb, in 2014.
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
10ppb
Highest yearly average, 2021 to 2026
2026 average: 8.2 ppb
Averaged by year, the highest was 10 ppb, in 2023, below EPA’s legal limit of 60 ppb. Its highest single sample was 23 ppb. In 2026, the latest year on file, its four samples averaged 8.2 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 6.8 ppb, in 2016.
What handles it
No certification claim covers this compound yet.
Fluoride
Forms or is added in treatment
0.37ppm
Highest yearly average, 2022 to 2023
Averaged by year, the highest was 0.37 ppm, in 2023, below EPA’s legal limit of 4.0 ppm. That was also the latest year on file. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.41 ppm, in 2012.
What handles it
- NSF/ANSI 58 look for “Fluoride Reduction”
- NSF/ANSI 53 look for “Fluoride”
Nitrate
Comes from the source
0.79ppm
Highest sample; found in 3 of 6
2025, one sample: 0.27 ppm
The highest sample, in 2024, was 0.79 ppm, below EPA’s legal limit of 10 ppm. In 2025, the latest year on file, its one sample was 0.27 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 1.4 ppm, in 2019.
What handles it
- NSF/ANSI 58 look for “Nitrate/Nitrite Reduction”
- NSF/ANSI 53 look for “Nitrate/Nitrite (30 ppm challenge)”
3 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
- Arsenic
- 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 58
Claim: Uranium
For: Uranium
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
None of the filters TapBuff has checked so far carry these claims. Search the certifier listings for the claim above.
Compare five-year costsHardness
Very hard, 285 mg/L (16.7 grains per gallon), at its one sampling point, 2019 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
No health-based violations on file with EPA since 2016.
What this report can’t tell you
Everything else. Uranium, total trihalomethanes (TTHM), haloacetic acids (HAA5), fluoride, nitrate, arsenic and chromium (total) results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Los Angeles Cwwd 40, Reg. 39 - Rock Creek’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 Feb. 24, 2020 to May 20, 2026.
Testing your own tap
The 3 labs California certifies closest to the area Los Angeles Cwwd 40, Reg. 39 - Rock Creek serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.
Eurofins Pomona
Pomona, CA · about 25 miles
Certified for bacteria, nitrate, lead and copper, metals, minerals and other inorganics, organic chemicals, disinfection byproducts, PFAS, radioactivity
EMSL Analytical, Inc. (LA Testing)
South Pasadena, CA · about 25 miles
Certified for bacteria, asbestos
Weck Laboratories, Inc.
City of Industry, CA · about 27 miles
Certified for bacteria, nitrate, lead and copper, metals, minerals and other inorganics, organic chemicals, disinfection byproducts, PFAS, radioactivity
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 Feb. 12, 2019 to May 14, 2025, read Oct. 10, 2026
- Limits and goals: each contaminant’s page, with its EPA source.
- How this page is built: methodology.
PWSID CA1910025. Rebuilt from EPA data on Oct. 18, 2026.
What to do next
- Read up on UraniumWhat each one does to health, where it comes from, and the certification claim that addresses it.About Uranium
- Get the utility’s own reportLos Angeles Cwwd 40, Reg. 39 - Rock Creek 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