State Well Water Guide
Wisconsin Private Well Water Guide
About 38% of Wisconsinites — approximately 2.2 million people — rely on private wells. Wisconsin's private well contamination landscape is shaped by its heavy dairy farming: nitrate contamination from manure and fertilizer application is pervasive, and bacterial contamination from livestock operations affects many shallow wells. Naturally occurring arsenic in specific glacial outwash deposits (particularly in eastern Wisconsin's Door Peninsula and Fox River Valley) is a documented concern. PFAS from industrial and military sources affect multiple communities. Wisconsin's Department of Natural Resources regulates well construction, and the state has conducted extensive well contamination surveys.
Testing Guidance
Wisconsin DNR recommends annual testing for coliform bacteria and nitrates for all private wells. Agricultural county well owners should test quarterly for nitrates during spring and fall application seasons. Eastern Wisconsin well owners should test for arsenic. Well owners near military facilities (Volk Field, Fort McCoy) should test for PFAS. All shallow dug well owners in agricultural areas should test more frequently.
What to Test For in Wisconsin
Total coliform bacteria and E. coli — annual minimum; quarterly for agricultural area wells
Nitrates — highest priority for all Wisconsin agricultural county well owners
Arsenic — eastern Wisconsin glacial outwash wells (Calumet, Outagamie, Winnebago, Brown, Kewaunee, and Door counties)
PFAS — near Volk Field, Fort McCoy, and industrial sites in the Fox River Valley
Iron and manganese — glacial drift wells throughout the state
Agricultural herbicides and pesticides — shallow wells near corn and potato fields
Bacteria from livestock — wells within a quarter mile of CAFOs and manure application fields
Common Contamination Risks in Wisconsin
Nitrate from dairy farming — Wisconsin's intensive dairy industry applies enormous volumes of liquid manure that leaches nitrates into shallow groundwater; one of the state's most persistent water quality challenges
Arsenic from glacial outwash — eastern Wisconsin's Fox River Valley has documented naturally elevated arsenic in glacial outwash wells; Kewaunee County has been a focal point of well contamination research
Bacterial contamination from manure — Kewaunee County has been the subject of national attention for private well contamination linked to nearby dairy operations; E. coli and other fecal bacteria are documented in many county wells
PFAS from industrial and military sources — Fox River Valley industrial history and military facilities
Iron and manganese from glacial sediments — common throughout Wisconsin
Contaminant Guides Relevant to WI Wells
PFAS
Synthetic Chemicals
EPA limit: 4 ppt
Lead
Heavy Metals
EPA limit: 15 ppb (action level)
Nitrates
Agricultural Chemicals
EPA limit: 10 mg/L
DBPs
Disinfection Byproducts
EPA limit: 80 µg/L (TTHMs) / 60 µg/L (HAA5)
Arsenic
Heavy Metals
EPA limit: 10 ppb
Hard Water
Minerals
EPA limit: No federal limit
Chlorine
Disinfection Chemicals
EPA limit: 4 mg/L (MRDL)
Microplastics
Emerging Contaminants
EPA limit: No federal limit
Bacteria
Microbial Contamination
EPA limit: Zero E. coli / < 1 coliform per 100 mL
Fluoride
Minerals
EPA limit: 4 mg/L (MCL) / 2 mg/L (Secondary MCL)
Chromium-6
Heavy Metals
EPA limit: 100 ppb (total chromium)
Copper
Heavy Metals
EPA limit: 1.3 mg/L (action level)
Radon
Radioactive Contaminants
EPA limit: No finalized MCL
Iron & Manganese
Minerals
EPA limit: 0.3 mg/L iron / 0.05 mg/L manganese (aesthetic SMCLs)
Atrazine
Agricultural Chemicals
EPA limit: 3 ppb (0.003 mg/L)
Uranium
Radioactive Contaminants
EPA limit: 30 µg/L (30 ppb)
Perchlorate
Industrial Chemicals
EPA limit: 0.056 mg/L (56 ppb)
VOCs
Industrial Chemicals
EPA limit: Varies by compound: benzene 5 ppb; TCE 5 ppb; PCE 5 ppb; vinyl chloride 2 ppb
Radium
Radioactive Contaminants
EPA limit: 5 pCi/L (combined Ra-226 + Ra-228)
Crypto & Giardia
Microbial Contamination
EPA limit: Zero (treatment technique standard)
Hydrogen Sulfide
Naturally Occurring Compounds
EPA limit: No MCL; Secondary MCL (aesthetic) of 0.05 mg/L
Selenium
Minerals
EPA limit: 50 ppb (0.05 mg/L)
Cadmium
Heavy Metals
EPA limit: 5 ppb (0.005 mg/L)
Mercury
Heavy Metals
EPA limit: 2 ppb (0.002 mg/L)
Barium
Heavy Metals
EPA limit: 2 mg/L
Find a Certified Lab in Wisconsin
Use the Wisconsin state-certified laboratory program to find accredited labs for private well testing. Always verify current certification before submitting samples.
WI Certified Lab Directory ↗Wisconsin Well Water FAQs
Related Pages
Data Sources & Provenance
All data on this page is sourced from official U.S. government or public datasets.
Quick Reference
State program
WI Certified Labs ↗EPA guidance
EPA Private Wells Program ↗State lab directory
WI Certified Labs ↗Minimum Annual Tests
Plus state-specific contaminants listed above
Other State Guides