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Castle Airport

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
150 people
Connections
134
Water source
Groundwater
Based in
Merced, CA
County
Merced
Owner
Local government
Hardness
Moderately hard
The 2 ZIP codes it serves

95301, 95388

The short answer

2 results are above the health goal. The worst: Lead, above the health goal. 1 health-based violation since 2016.

What handles it

What was found

Lead and copper: EPA SDWIS monitoring periods ending 1992 to 2023.

Arsenic, nitrate, total trihalomethanes (TTHM), fluoride, chromium (total) and haloacetic acids (HAA5): California’s own results, samples taken from May 20, 2020 to June 17, 2026, with EPA’s 2012 to 2019 file for earlier years.

Above the health goal2

Lead

Comes from pipes, often your own

Above the health goal

6.9ppb

90th percentile, 2021 to 2023

In the latest period, 9 in 10 homes sampled were at or below 6.9 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

Arsenic

Comes from the source

Above the health goal

4.0ppb

Highest yearly average, 2022 to 2026

2026 average: 3.6 ppb

Averaged by year, the highest was 4.0 ppb, in 2023: below EPA’s legal limit of 10 ppb, but above its health goal of zero. Its highest single sample was 4.7 ppb. In 2026, the latest year on file, its two samples averaged 3.6 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 4.4 ppb, in 2019.

What handles it

  • NSF/ANSI 58 look for “Arsenic (Pentavalent)<=50 ppb Reduction”
  • NSF/ANSI 53 look for “Arsenic (Pentavalent)<=50 ppb Reduction”

Below EPA’s limits3

Nitrate

Comes from the source

Below EPA’s limits

5.0ppm

Highest sample; found in 14 of 14

2026 average: 4.3 ppm

The highest sample, in 2026, was 5.0 ppm, below EPA’s legal limit of 10 ppm. That was also the latest year on file, and its two samples averaged 4.3 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 4.8 ppm, in 2013.

What handles it

  • NSF/ANSI 58 look for “Nitrate/Nitrite Reduction”
  • NSF/ANSI 53 look for “Nitrate/Nitrite (30 ppm challenge)”

Total trihalomethanes (TTHM)

Forms or is added in treatment

Below EPA’s limits

9.5ppb

Highest yearly average, 2020 to 2026

Averaged by year, the highest was 9.5 ppb, in 2026, below EPA’s legal limit of 80 ppb. That was also the latest year on file. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 2.8 ppb, in 2017.

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

Below EPA’s limits

0.13ppm

Highest yearly average, 2023 to 2026

2026 average: 0.05 ppm

Averaged by year, the highest was 0.13 ppm, in 2023, below EPA’s legal limit of 4.0 ppm. Its highest single sample was 0.14 ppm. In 2026, the latest year on file, its two samples averaged 0.05 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.28 ppm, in 2019.

What handles it

2 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Chromium (total)
  • 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: Lead Reduction, Arsenic (Pentavalent)<=50 ppb Reduction

    For: Lead, Arsenic

    Other certifiers’ wording: Arsenic (III) (50 ppb influent level)

  • NSF/ANSI 58

    Claims: Lead Reduction, Arsenic (Pentavalent)<=50 ppb Reduction

    For: Lead, Arsenic

    Other certifiers’ wording: Arsenic (Pentavalent)<=300 ppb Reduction; Arsenic (V) (300 ppb influent level)

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

Compare five-year costs

The best water filters for lead, ranked

The best reverse osmosis systems, ranked

Hardness

Moderately hard, typically 69 mg/L (4 grains per gallon), across 2 sampling points, 2019 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.

Softeners compared at 4 grains per gallon, salt includedSoftener or salt-free conditioner?California water hardness, utility by utility

Violations since 2016

Contaminant or ruleTypePeriodMeasuredStatus
Lead and Copper Rule RevisionsThe required inventory of lead service lines was not completed or submitted on time.EPA: LSL InventoryOct. 17, 2024—Unaddressed
Health-based violations only. Resolved and archived mean the utility returned to compliance or the state closed the record. 5 monitoring or reporting violations not shown.

What this report can’t tell you

  • Everything else. Arsenic, nitrate, total trihalomethanes (TTHM), fluoride, chromium (total) and haloacetic acids (HAA5) results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. Castle Airport’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 20, 2020 to June 17, 2026.

Testing your own tap

Castle Airport’s results are for the water it sends out. What your own service line, solder and fixtures add shows up only in a test of your tap, by a lab California certifies.

The 3 labs California certifies closest to the area Castle Airport serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.

  • Microbac Laboratories, Inc. - Turlock

    Turlock, CA · about 17 miles

    Certified for bacteria, nitrate, lead and copper, metals, minerals and other inorganics, organic chemicals, disinfection byproducts, radioactivity

    (707) 822-4649

  • Certified Laboratories - Turlock

    Turlock, CA · about 17 miles

    Certified for bacteria

    (209) 664-1100

  • Aemtek, Inc.

    Modesto, CA · about 31 miles

    Certified for bacteria

    (510) 979-1979

All 145 certified labs for California

Sources

PWSID CA2410700. Rebuilt from EPA data on Oct. 18, 2026.

Also in Merced County

All California utilities

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