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County Service Area 7

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
300 people
Connections
69
Water source
Surface water
Based in
Redwood City, CA
County
San Mateo
Owner
Local government
Hardness
Very hard
The ZIP code it serves

94020

The short answer

1 result is above EPA’s legal limit, and 2 more are above the health goal. The worst: Haloacetic acids (HAA5), above the legal limit. 6 health-based violations since 2016.

What handles it

What was found

Lead and copper: EPA SDWIS monitoring periods ending 2022 to 2028.

Haloacetic acids (HAA5), arsenic, total trihalomethanes (TTHM), nitrate, fluoride and chromium (total): California’s own results, samples taken from Jan. 6, 2020 to June 22, 2026, with EPA’s 2012 to 2019 file for earlier years.

Above the legal limit1

Haloacetic acids (HAA5)

Forms or is added in treatment

Above the legal limit

60ppb

Highest yearly average, 2020 to 2026

Averaged by year, the highest was 60 ppb, in 2026, below EPA’s legal limit of 60 ppb. Its highest single sample was 102 ppb. That was also the latest year on file. EPA judges this limit at each sampling point, and recorded violations for haloacetic acids (HAA5) at this utility in 2020 and 2025. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 59.5 ppb, in 2019.

What handles it

No certification claim covers this compound yet.

Above the health goal2

Arsenic

Comes from the source

Above the health goal

1.8ppb

Highest yearly average, 2020 to 2026

2026, one sample: 1.3 ppb

Averaged by year, the highest was 1.8 ppb, in 2021: below EPA’s legal limit of 10 ppb, but above its health goal of zero. In 2026, the latest year on file, its one sample was 1.3 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 2.0 ppb, in 2016.

What handles it

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

Lead

Comes from pipes, often your own

Above the health goal

1.8ppb

90th percentile, 2026 to 2028

In the latest period, 9 in 10 homes sampled were at or below 1.8 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

Below EPA’s limits4

Total trihalomethanes (TTHM)

Forms or is added in treatment

Below EPA’s limits

69.5ppb

Highest yearly average, 2020 to 2026

2026 average: 52.5 ppb

Averaged by year, the highest was 69.5 ppb, in 2022, below EPA’s legal limit of 80 ppb. Its highest single sample was 102 ppb. In 2026, the latest year on file, its two samples averaged 52.5 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 103 ppb, in 2018, and EPA recorded violations in 2017 and 2018.

What handles it

  • NSF/ANSI 53 look for “Trihalomethanes (TTHM) Reduction”
  • NSF/ANSI 58 look for “Trihalomethanes (TTHM) Reduction”

Nitrate

Comes from the source

Below EPA’s limits

1.0ppm

Highest sample; found in 6 of 29

2026 average: 0.11 ppm

The highest sample, in 2020, was 1.0 ppm, below EPA’s legal limit of 10 ppm. In 2026, the latest year on file, its three samples averaged 0.11 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 0.76 ppm, in 2018.

What handles it

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

Fluoride

Forms or is added in treatment

Below EPA’s limits

0.4ppm

Highest yearly average, 2020 to 2026

2026, one sample: 0.2 ppm

Averaged by year, the highest was 0.4 ppm, in 2020, below EPA’s legal limit of 4.0 ppm. In 2026, 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 0.46 ppm, in 2013.

What handles it

Chromium (total)

Comes from the source

Below EPA’s limits

3.2ppb

Highest yearly average, 2020 to 2026

2026: not found

Averaged by year, the highest was 3.2 ppb, in 2020, below EPA’s legal limit of 100 ppb. In 2026, the latest year on file, it wasn’t found in its one sample.

What handles it

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, Lead Reduction

    For: Arsenic, Lead

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

  • NSF/ANSI 58

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

    For: Arsenic, Lead

    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 reverse osmosis systems, ranked

The best water filters for lead, ranked

Hardness

Very hard, 359 mg/L (21 grains per gallon), at its one sampling point, 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 21 grains per gallon, salt includedSoftener or salt-free conditioner?California water hardness, utility by utility

Violations since 2016

Contaminant or ruleTypePeriodMeasuredStatus
Total Haloacetic Acids (HAA5)The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, AverageJan. 1, 2025 to March 31, 20250.064 MG/LResolved
Total Haloacetic Acids (HAA5)The running average was above the legal limit.EPA: Maximum Contaminant Level Violation, AverageJan. 1, 2020 to March 31, 20200.073 MG/LResolved
TTHMThe running average was above the legal limit.EPA: Maximum Contaminant Level Violation, AverageApril 1, 2018 to June 30, 20180.12 MG/LResolved
TTHMThe running average was above the legal limit.EPA: Maximum Contaminant Level Violation, AverageJan. 1, 2018 to March 31, 20180.1 MG/LResolved
TTHMThe running average was above the legal limit.EPA: Maximum Contaminant Level Violation, AverageOct. 1, 2017 to Dec. 31, 20170.091 MG/LResolved
TTHMThe running average was above the legal limit.EPA: Maximum Contaminant Level Violation, AverageJuly 1, 2017 to Sept. 30, 20170.09 UG/LResolved
Health-based violations only. Resolved and archived mean the utility returned to compliance or the state closed the record.

What this report can’t tell you

  • Everything else. Haloacetic acids (HAA5), arsenic, total trihalomethanes (TTHM), nitrate, fluoride and chromium (total) results here are California’s own from 2020 on, with EPA’s national file for 2012 to 2019. County Service Area 7’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. 6, 2020 to June 22, 2026.

Testing your own tap

County Service Area 7’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 County Service Area 7 serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.

  • San Mateo County Public Health Laboratory

    San Mateo, CA · about 18 miles

    Certified for bacteria

    (650) 573-2500

  • Torrent Laboratory, Inc

    Milpitas, CA · about 21 miles

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

    (408) 263-5258

  • AEMTEK, Inc

    Fremont, CA · about 22 miles

    Certified for bacteria, minerals and other inorganics

    (510) 979-1979

All 145 certified labs for California

Sources

PWSID CA4100509. Rebuilt from EPA data on Oct. 18, 2026.

Also in San Mateo County

All California utilities

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