Skip to content
TapBuff
ZIP

Colby Waterworks

What EPA’s and Wisconsin’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
1,829 people
Connections
700
Water source
Groundwater
Based in
Colby, WI
County
Marathon
Owner
Local government
Hardness
Varies by source
The ZIP code it serves

54421

The short answer

1 result is above the limit’s level with no violation recorded, and 2 more are above the health goal. The worst: Uranium, above the limit’s level, no violation. No health-based violations on file since 2016.

What handles it

What was found

Lead and copper: EPA SDWIS monitoring periods ending 2002 to 2023.

Copper: EPA’s file records a utility’s copper only when it exceeds the action level. The last here was 2.1 ppm, for the period ending Dec. 31, 1993. None since is on file, so it is not counted as a current finding.

Arsenic, nitrate, total trihalomethanes (TTHM), fluoride, haloacetic acids (HAA5) and chromium (total): Wisconsin’s own results, samples taken from Jan. 7, 2020 to Sept. 1, 2026, with EPA’s 2012 to 2019 file for earlier years.

Uranium: EPA’s compliance monitoring file, samples taken from Oct. 24, 2014 to Sept. 18, 2019. Newer results are in the utility’s annual water quality report.

Above the limit’s level, no violation recorded1

Uranium

Comes from the source

Above the limit’s level, no violation

36.8ppb

Highest yearly average, 2014 to 2019

2019, one sample: 10.9 ppb

Averaged by year, the highest was 36.8 ppb, in 2017, above EPA’s legal limit of 30 ppb. Its highest single sample was 38.3 ppb. In 2019, the latest year on file, its one sample was 10.9 ppb. EPA judges this limit on running averages at each sampling point, and recorded no violation for uranium at this utility from 2012 to 2019. Results like these with no violation often include water sampled before treatment or blending; the utility’s annual report says what reaches the tap.

What handles it

Above the health goal2

Lead

Comes from pipes, often your own

Above the health goal

0.95ppb

90th percentile, 2023

In the latest period, 9 in 10 homes sampled were at or below 0.95 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

0.29ppb

Highest yearly average, 2020 to 2026

2026: not found

Averaged by year, the highest was 0.29 ppb, in 2020: below EPA’s legal limit of 10 ppb, but above its health goal of zero. Its highest single sample was 0.37 ppb. In 2026, the latest year on file, it wasn’t found in any of its two samples. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.3 ppb, in 2014.

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 limits4

Nitrate

Comes from the source

Below EPA’s limits

8.9ppm

Highest sample; found in 9 of 9

2025, one sample: 4.3 ppm

The highest sample, in 2020, was 8.9 ppm, below EPA’s legal limit of 10 ppm. In 2025, the latest year on file, its one sample was 4.3 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest sample of 9.4 ppm, in 2017.

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

18.8ppb

Highest yearly average, 2020 to 2026

Averaged by year, the highest was 18.8 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 17 ppb, in 2014.

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

0.7ppm

Highest yearly average, 2020 to 2026

Averaged by year, the highest was 0.7 ppm, in 2026, below EPA’s legal limit of 4.0 ppm. Its highest single sample was 0.8 ppm. That was also the latest year on file. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.53 ppm, in 2012.

What handles it

Haloacetic acids (HAA5)

Forms or is added in treatment

Below EPA’s limits

4.6ppb

Highest yearly average, 2020 to 2026

2026, one sample: 2.4 ppb

Averaged by year, the highest was 4.6 ppb, in 2020, below EPA’s legal limit of 60 ppb. In 2026, the latest year on file, its one sample was 2.4 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.

One compound tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.
  • Chromium (total)

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

    For: Uranium, 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

Hard to very hard depending on the source, 125 to 230 mg/L (7.3 to 13.5 grains per gallon), across 3 sampling points, 2017 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, salt includedSoftener or salt-free conditioner?Wisconsin 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. Arsenic, nitrate, total trihalomethanes (TTHM), fluoride, haloacetic acids (HAA5) and chromium (total) results here are Wisconsin’s own from 2020 on, with EPA’s national file for 2012 to 2019. Uranium comes from EPA’s file alone, which ends in 2019. Colby Waterworks’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; Wisconsin’s results run from Jan. 7, 2020 to Sept. 1, 2026; EPA’s compliance samples are from Oct. 24, 2014 to Sept. 18, 2019.

Testing your own tap

Colby Waterworks’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 Wisconsin certifies.

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

  • AgSource Laboratories

    Marshfield, WI · about 18 miles

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

    (715) 898-1402

  • Clark County Health Department

    Neillsville, WI · about 30 miles

    Certified for bacteria

    (715) 743-5105

  • Lincoln County Health Department

    Merrill, WI · about 33 miles

    Certified for bacteria, nitrate

    (715) 536-0307

Wisconsin State Laboratory of Hygiene: Well water test kits ordered by phone and shipped free; you pay to mail the sample back, and the lab bills you after testing. Tests run from bacteria alone to a homeowner package covering bacteria, nitrate, fluoride, metals, hardness, volatile organic compounds and atrazine. Bacteria is $35, nitrate $35, lead $38, and the homeowner package $450, as of July 1, 2026. Public Environmental and Water Testing Prices, Wisconsin State Laboratory of Hygiene.

All 156 certified labs for Wisconsin

Sources

PWSID WI7370169. Rebuilt from EPA data on Oct. 18, 2026.

Also in Marathon County

All Wisconsin utilities

What to do next