Oslo

What EPA’s and Minnesota’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: 242 people
Connections: 186
Water source: Groundwater bought from another system
Based in: Oslo, MN
County: Marshall
Owner: Local government

The ZIP code it serves

56744

The short answer

Nothing in EPA’s and Minnesota’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), nitrate and total trihalomethanes (TTHM): Minnesota’s yearly summaries per water system, 2023 to 2025.

Below EPA’s limits3

Haloacetic acids (HAA5)

Forms or is added in treatment

Below EPA’s limits

8.2ppb

Highest yearly average, 2023 to 2025

2025: not found

Averaged by year, the highest was 8.2 ppb, in 2024, below EPA’s legal limit of 60 ppb. In 2025, the latest year on file, it wasn’t found.

What handles it

No certification claim covers this compound yet.

Nitrate

Comes from the source

Below EPA’s limits

0.9ppm

Highest yearly average, 2023 to 2025

2025 average: 0.9 ppm

Averaged by year, the highest was 0.9 ppm, in 2023, below EPA’s legal limit of 10 ppm. In 2025, the latest year on file, it averaged 0.9 ppm.

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

2.9ppb

Highest yearly average, 2023 to 2025

2025 average: 0.7 ppb

Averaged by year, the highest was 2.9 ppb, in 2024, below EPA’s legal limit of 80 ppb. In 2025, the latest year on file, it averaged 0.7 ppb.

What handles it

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

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

Lead

Violations since 2016

No health-based violations on file with EPA since 2016. There is 1 monitoring or reporting violation: a sample missed, late or not reported.

What this report can’t tell you

Everything else. Haloacetic acids (HAA5), nitrate and total trihalomethanes (TTHM) results here are Minnesota’s own yearly summaries from 2023 on, with EPA’s national file for 2012 to 2019. Oslo’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; Minnesota’s yearly summaries cover 2023 to 2025.

Testing your own tap

Oslo’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 Minnesota certifies.

No lab Minnesota certifies is within 75 miles of the area Oslo serves on the state’s list. Some take samples by mail; the state’s page lists them all.

All 24 certified labs for Minnesota