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City of Modesto - Grayson

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
917 people
Connections
278
Water source
Groundwater
Based in
Modesto, CA
County
Stanislaus
Owner
Local government
Hardness
Very hard
The ZIP code it serves

95363

The short answer

3 results are above the health goal. The worst: Nitrate, above the health goal. No health-based violations on file since 2016.

What handles it

What was found

Nitrate, arsenic, uranium, total trihalomethanes (TTHM), chromium (total), haloacetic acids (HAA5) and fluoride: California’s own results, samples taken from Jan. 7, 2020 to June 30, 2026, with EPA’s 2012 to 2019 file for earlier years.

Above the health goal3

Nitrate

Comes from the source

Above the health goal

21ppm

Highest sample; found in 472 of 474

2026 average: 5.4 ppm

From 2020 to 2024, at least 25 samples were above EPA’s legal limit of 10 ppm, the highest 21 ppm in 2022. The next sample at the same point, within 30 days, kept the average above the limit for 17; eight have no follow-up sample on file within 30 days. 10 ppm is also EPA’s health goal. In 2026, the latest year on file, its 38 samples averaged 5.4 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 22.7 ppm, in 2016.

What handles it

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

Arsenic

Comes from the source

Above the health goal

4.5ppb

Highest yearly average, 2020 to 2026

2026: not found

Averaged by year, the highest was 4.5 ppb, in 2020: below EPA’s legal limit of 10 ppb, but above its health goal of zero. Its highest single sample was 5.0 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 1.3 ppb, in 2017.

What handles it

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

Uranium

Comes from the source

Above the health goal

3.3ppb

Highest yearly average, 2020 to 2026

Averaged by year, the highest was 3.3 ppb, in 2026: below EPA’s legal limit of 30 ppb, but above its health goal of zero. That was also the latest year on file. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 2.9 ppb, in 2015.

What handles it

Below EPA’s limits3

Total trihalomethanes (TTHM)

Forms or is added in treatment

Below EPA’s limits

65.6ppb

Highest yearly average, 2020 to 2026

2026 average: 10.7 ppb

Averaged by year, the highest was 65.6 ppb, in 2024, below EPA’s legal limit of 80 ppb. Its highest single sample was 175 ppb. In 2026, the latest year on file, its three samples averaged 10.7 ppb. EPA recorded no violation for total trihalomethanes (TTHM) at this utility since 2020. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 4.6 ppb, in 2013.

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

Below EPA’s limits

21ppb

Highest yearly average, 2020 to 2026

2026, one sample: 18 ppb

Averaged by year, the highest was 21 ppb, in 2025, below EPA’s legal limit of 100 ppb. In 2026, the latest year on file, its one sample was 18 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 20.5 ppb, in 2017.

What handles it

Haloacetic acids (HAA5)

Forms or is added in treatment

Below EPA’s limits

7.5ppb

Highest yearly average, 2020 to 2026

2026 average: 1.8 ppb

Averaged by year, the highest was 7.5 ppb, in 2024, below EPA’s legal limit of 60 ppb. Its highest single sample was 13.4 ppb. In 2026, the latest year on file, its two samples averaged 1.8 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 4.6 ppb, in 2014.

What handles it

No certification claim covers this compound yet.

2 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Fluoride
  • 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: Nitrate/Nitrite (30 ppm challenge), Arsenic (Pentavalent)<=50 ppb Reduction

    For: Nitrate, Arsenic

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

  • NSF/ANSI 58

    Claims: Nitrate/Nitrite Reduction, Arsenic (Pentavalent)<=50 ppb Reduction, Uranium

    For: Nitrate, Arsenic, Uranium

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

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

Compare five-year costs

The best reverse osmosis systems, ranked

Hardness

Very hard, typically 778 mg/L (45.5 grains per gallon), across 4 sampling points, 2020 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 45.5 grains per gallon, salt includedSoftener or salt-free conditioner?California water hardness, utility by utility

Violations since 2016

No health-based violations on file with EPA since 2016.

What this report can’t tell you

  • Everything else. Nitrate, arsenic, uranium, total trihalomethanes (TTHM), chromium (total), haloacetic acids (HAA5) and fluoride results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. City of Modesto - Grayson’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. 7, 2020 to June 30, 2026.

Testing your own tap

City of Modesto - Grayson’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 City of Modesto - Grayson serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.

  • Certified Laboratories - Turlock

    Turlock, CA · about 19 miles

    Certified for bacteria

    (209) 664-1100

  • Institute of Environmental Health, Inc. dba IEH-JL Analytical

    Modesto, CA · about 19 miles

    Certified for bacteria, nitrate, minerals and other inorganics

    (209) 538-8111

  • Microbac Laboratories, Inc. - Turlock

    Turlock, CA · about 20 miles

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

    (707) 822-4649

All 145 certified labs for California

Sources

PWSID CA5010033. Rebuilt from EPA data on Oct. 18, 2026.

Towns it serves

Also in Stanislaus County

All California utilities

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