Winona County, Minnesota

Arsenic: 1 of 97 sampled wells (1%) above the EPA limit of 10 µg/L. Nitrate: 1 of 23 sampled wells (4%) above the EPA limit of 10 mg/L as N. Samples 1963-06-21 to 2024-07-10; updated 2026-10-18. Source: Water Quality Portal (USGS, EPA, NWQMC), siteType=Well.

What wells in this county have measured for arsenic and nitrate. A local picture only: test your own well to know your water.

Arsenic

1 of 97 sampled wells (1%) had a latest result above the EPA limit of 10 µg/L.

Median (latest per well): 0 µg/L
90th percentile: 0.433 µg/L
Highest: 14.8 µg/L
Non-detects: 54 wells' latest result was "not detected" with no detection limit reported; they are counted as below the limit.
Samples: 108, 1980-02-13 to 2024-07-10
Source: Water Quality Portal (USGS, EPA, NWQMC), siteType=Well, downloaded 2026-10-18

Nitrate

1 of 23 sampled wells (4%) had a latest result above the EPA limit of 10 mg/L as N.

Median (latest per well): 0.1 mg/L as N
90th percentile: 2.5 mg/L as N
Highest: 16 mg/L as N
Non-detects: 7 wells' latest result was "not detected" with no detection limit reported; they are counted as below the limit.
Samples: 23, 1963-06-21 to 2013-09-16
Source: Water Quality Portal (USGS, EPA, NWQMC), siteType=Well, downloaded 2026-10-18

Includes monitoring, research and private wells reported to the Water Quality Portal. Non-detects count only when the lab's detection limit is at or below the EPA limit. Method: data rules.

What to do next

Test your own well. County numbers cannot tell you what is in your water. See which tests fit your well.
Use a lab certified by Minnesota. Certified labs in Minnesota.
Compare your results with the EPA limits (arsenic 10 µg/L, nitrate 10 mg/L as N). If a result is above a limit, contact your county or state health department.
If a result is high: arsenic guide · nitrate guide · bacteria guide · salesperson checklist.
Test again every year for bacteria and nitrate. Get a yearly reminder.