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Lake Margaret Water System

What EPA’s and Washington’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
406 people
Connections
152
Water source
Surface water
Based in
Carnation, WA
County
King
Owner
Private
Hardness
Soft
The ZIP code it serves

98019

The short answer

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

What handles it

What was found

Lead and copper: EPA SDWIS monitoring periods ending 2007 to 2023.

Arsenic, total trihalomethanes (TTHM), haloacetic acids (HAA5), nitrate, chromium (total) and fluoride: Washington’s own results, samples taken from Feb. 5, 2020 to Sept. 21, 2026, with EPA’s 2012 to 2019 file for earlier years.

Above the health goal2

Arsenic

Comes from the source

Above the health goal

7.1ppb

Highest yearly average, 2020 to 2026

2026 average: 5.6 ppb

Averaged by year, the highest was 7.1 ppb, in 2021: below EPA’s legal limit of 10 ppb, but above its health goal of zero. Its highest single sample was 19.2 ppb. In 2026, the latest year on file, its six samples averaged 5.6 ppb. EPA recorded no violation for arsenic at this utility since 2020. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 18 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”

Lead

Comes from pipes, often your own

Above the health goal

1.8ppb

90th percentile, 2021 to 2023

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 limits3

Total trihalomethanes (TTHM)

Forms or is added in treatment

Below EPA’s limits

28.5ppb

Highest yearly average, 2020 to 2026

2026, one sample: 17.8 ppb

Averaged by year, the highest was 28.5 ppb, in 2024, below EPA’s legal limit of 80 ppb. In 2026, the latest year on file, its one sample was 17.8 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 33.3 ppb, in 2012.

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

Below EPA’s limits

14.3ppb

Highest yearly average, 2020 to 2025

2025, one sample: 7.1 ppb

Averaged by year, the highest was 14.3 ppb, in 2024, below EPA’s legal limit of 60 ppb. In 2025, the latest year on file, its one sample was 7.1 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 14.3 ppb, in 2015.

What handles it

No certification claim covers this compound yet.

Nitrate

Comes from the source

Below EPA’s limits

0.23ppm

Highest sample; found in 1 of 14

2026: not found

The highest sample, in 2023, was 0.23 ppm, below EPA’s legal limit of 10 ppm. In 2026, the latest year on file, it wasn’t found in any of its three samples.

What handles it

  • NSF/ANSI 58 look for “Nitrate/Nitrite Reduction”
  • NSF/ANSI 53 look for “Nitrate/Nitrite (30 ppm challenge)”
2 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Chromium (total)
  • Fluoride

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

Soft, 12 mg/L (0.7 grains per gallon), at its one sampling point, in 2020.

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 0.7 grains per gallon, salt includedSoftener or salt-free conditioner?Washington water hardness, utility by utility

Violations since 2016

No health-based violations on file with EPA since 2016. There are 46 monitoring or reporting violations: a sample missed, late or not reported.

What this report can’t tell you

  • Everything else. Arsenic, total trihalomethanes (TTHM), haloacetic acids (HAA5), nitrate, chromium (total) and fluoride results here are Washington’s own from 2020 on, with EPA’s national file for 2012 to 2019. Lake Margaret Water System’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; Washington’s results run from Feb. 5, 2020 to Sept. 21, 2026.

Testing your own tap

Lake Margaret Water System’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 Washington certifies.

The 3 labs Washington certifies closest to the area Lake Margaret Water System serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.

  • OnSite Environmental, Inc.

    Redmond, WA · about 13 miles

    Certified for lead and copper, metals, minerals and other inorganics

    (425) 883-3881

  • Brooks Applied Labs, LLC

    Seattle, WA · about 21 miles

    Certified for lead and copper, metals

    (206) 753-6119

  • IEH Analytical Laboratories

    Seattle, WA · about 21 miles

    Certified for nitrate, lead and copper, metals, minerals and other inorganics, PFAS

    (206) 632-2715

All 84 certified labs for Washington

Sources

PWSID WA5344200. Rebuilt from EPA data on Oct. 18, 2026.

Also in King County

All Washington utilities

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