Skip to content
TapBuff
ZIP

Twanoh Terrace Water Co

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
75 people
Connections
30
Water source
Groundwater
Based in
Union, WA
County
Mason
Owner
Local government
The ZIP code it serves

98528

The short answer

Nothing in EPA’s and Washington’s records for this utility is above a health goal. That covers nitrate, arsenic and other regulated chemicals, plus lead and copper, not everything. No health-based violations on file since 2016.

What was found

Nitrate: Washington’s own results, samples taken from April 22, 2020 to Sept. 1, 2026, with EPA’s 2012 to 2019 file for earlier years.

Chromium (total), arsenic and fluoride: EPA’s compliance monitoring file, samples taken from July 10, 2012 to April 12, 2018. Newer results are in the utility’s annual water quality report.

Below EPA’s limits1

Chromium (total)

Comes from the source

Below EPA’s limits

1.0ppb

Highest yearly average, 2012 to 2018

2018: not found

Averaged by year, the highest was 1.0 ppb, in 2015, below EPA’s legal limit of 100 ppb. In 2018, the latest year on file, it wasn’t found in its one sample.

What handles it

4 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Arsenic
  • Fluoride
  • Lead
  • Nitrate

Violations since 2016

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

What this report can’t tell you

  • Everything else. Nitrate results here are Washington’s own from 2020 on, with EPA’s national file for 2012 to 2019. Chromium (total), arsenic and fluoride come from EPA’s file alone, which ends in 2019. Twanoh Terrace Water Co’s own annual report, which it must send you every year, has newer results for those and 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 April 22, 2020 to Sept. 1, 2026; EPA’s compliance samples are from July 10, 2012 to April 12, 2018.

Testing your own tap

Twanoh Terrace Water Co’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 Twanoh Terrace Water Co serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.

  • Thurston County Health Department Laboratory

    Olympia, WA · about 23 miles

    Certified for bacteria, nitrate

    (360) 867-2631

  • Spectra Laboratories - Kitsap, LLC

    Poulsbo, WA · about 25 miles

    Certified for bacteria, nitrate, minerals and other inorganics

    (360) 779-5141

  • Olympic Analytical LLC dba Vanguard Laboratory

    Olympia, WA · about 26 miles

    Certified for bacteria, nitrate

    (360) 967-7010

All 84 certified labs for Washington

Sources

PWSID WA5360190. Rebuilt from EPA data on Oct. 18, 2026.

Also in Mason County

All Washington utilities

What to do next