City of Onaga

What EPA’s and Kansas’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: 671 people
Connections: 380
Water source: Groundwater
Based in: Onaga, KS
County: Pottawatomie
Owner: Local government
Hardness: Very hard

The ZIP code it serves

66521

The short answer

Nothing in EPA’s and Kansas’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

Haloacetic acids (HAA5), fluoride, total trihalomethanes (TTHM), chromium (total), arsenic and nitrate: Kansas’s own results, samples taken from March 9, 2020 to Sept. 14, 2026, with EPA’s 2012 to 2019 file for earlier years.

Below EPA’s limits4

Haloacetic acids (HAA5)

Forms or is added in treatment

Below EPA’s limits

7.0ppb

Highest yearly average, 2020 to 2025

2025, one sample: 5.3 ppb

Averaged by year, the highest was 7.0 ppb, in 2024, below EPA’s legal limit of 60 ppb. In 2025, the latest year on file, its one sample was 5.3 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 6.4 ppb, in 2019.

What handles it

No certification claim covers this compound yet.

Fluoride

Forms or is added in treatment

Below EPA’s limits

0.4ppm

Highest yearly average, 2020 to 2026

2026, one sample: 0.3 ppm

Averaged by year, the highest was 0.4 ppm, in 2023, below EPA’s legal limit of 4.0 ppm. In 2026, the latest year on file, its one sample was 0.3 ppm. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 0.89 ppm, in 2017.

What handles it

NSF/ANSI 58 look for “Fluoride Reduction”
NSF/ANSI 53 look for “Fluoride”

Total trihalomethanes (TTHM)

Forms or is added in treatment

Below EPA’s limits

4.7ppb

Highest yearly average, 2020 to 2026

2026, one sample: 3.7 ppb

Averaged by year, the highest was 4.7 ppb, in 2024, below EPA’s legal limit of 80 ppb. In 2026, the latest year on file, its one sample was 3.7 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 5.5 ppb, in 2016.

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

2.1ppb

Highest yearly average, 2020 to 2026

2026, one sample: 1.2 ppb

Averaged by year, the highest was 2.1 ppb, in 2020, below EPA’s legal limit of 100 ppb. In 2026, the latest year on file, its one sample was 1.2 ppb. Earlier, from 2012 to 2019, EPA’s file shows a highest yearly average of 1.8 ppb, in 2014.

What handles it

NSF/ANSI 58 look for “Chromium (Hexavalent) Reduction”
NSF/ANSI 53 look for “Chromium Reduction”

3 compounds tested and not foundBelow the reporting level in every sample. Not found is not the same as zero.

Arsenic
Lead
Nitrate

Hardness

Very hard, 260 mg/L (15.2 grains per gallon), at its one sampling point, 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 at 15.2 grains per gallon, salt included Softener or salt-free conditioner?Kansas 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. Haloacetic acids (HAA5), fluoride, total trihalomethanes (TTHM), chromium (total), arsenic and nitrate results here are Kansas’s own from 2020 on, with EPA’s national file for 2012 to 2019. City of Onaga’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; Kansas’s results run from March 9, 2020 to Sept. 14, 2026.

Testing your own tap

City of Onaga’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 Kansas certifies.

The lab Kansas certifies closest to the area City of Onaga serves, in a straight line. Call first: certification is test by test, and not every lab takes samples from homeowners.