Nitrate In Drinking Water In Wisconsin
What residents of Wisconsin need to know about nitrate in drinking water — including how it enters water, which utilities have documented violations, and what steps to take.
Source: EPA SDWIS, Wisconsin Department of Natural Resources (WDNR), CDC · Last reviewed: 2025-01-01
Quick Answer
Is nitrate in drinking water a real concern in Wisconsin?
Yes — Wisconsin has extensively documented agricultural nitrate contamination in private wells, with Kewaunee County on karst soils becoming a nationally recognized example of manure-driven nitrate and pathogen contamination in private wells.
Is this mostly a public-water issue, a private-well issue, or both?
Primarily private well users in agricultural counties across Wisconsin; Kewaunee, Brown, and Manitowoc Counties have the most documented contamination. The Central Sands region also has documented nitrate from potato and vegetable irrigation.
What is the main reason residents should care?
Wisconsin is a major dairy state. Kewaunee County's combination of intensive dairy operations and karst limestone geology has produced some of the most extensively documented private-well nitrate and pathogen contamination in the nation — a case study for agricultural water contamination risks.
Key Facts
| EPA Nitrate MCL | 10 mg/L as N |
| Kewaunee County | Nationally documented case — dairy manure on karst limestone contaminates private wells |
| Central Sands | Adams, Waushara, Portage Counties — potato irrigation on sandy soils elevates nitrate |
| WDNR testing programs | Wisconsin has funded private well testing assistance programs |
| State oversight | Wisconsin Department of Natural Resources (WDNR) |
Why This Matters in Wisconsin
Wisconsin's dairy industry is one of the largest in the nation, and the state's agricultural landscape includes significant manure application to cropland. Kewaunee County in northeast Wisconsin overlies karst limestone, allowing dairy manure applied to fields to move rapidly through sinkholes and fractures into private wells. WDNR has documented that a significant percentage of Kewaunee County private wells have detectable nitrate and pathogens. The Central Sands region (Adams, Waushara, and Portage Counties) has documented nitrate from irrigation and potato production over highly permeable sandy soils. Wisconsin has funded private well testing programs and nutrient management planning for dairy farms, but the problem is persistent given the state's agricultural intensity.
Historical Context
Kewaunee County has become a nationally known case study in agricultural water contamination. Research documented that a high percentage of private wells in Kewaunee County showed nitrate and pathogen contamination linked to dairy manure applications on karst soils. The case has influenced national discussions about agricultural water quality regulation.
Critical — Infants Under 6 Months
Do not use tap water that exceeds 10 mg/L nitrate-nitrogen to prepare infant formula or feed infants under six months. Boiling will concentrate nitrate — do not boil. Use bottled water or a certified reverse osmosis system (NSF/ANSI 58) until the issue is resolved.
Wisconsin Utilities With Nitrate Violation Records
The utilities listed below have at least one nitrate violation on record in EPA's SDWIS database. Violations may be open or resolved — see individual utility pages for current status and risk level.
Milwaukee Waterworks
Milwaukee · 626,000 served
Racine Waterworks
Racine · 105,100 served
Kenosha Water Utility
Kenosha · 99,218 served
Appleton Waterworks
Menasha · 74,511 served
Waukesha Water Utility
Waukesha · 70,718 served
West Allis Waterworks
West Allis · 63,240 served
Sheboygan Water Utilities
Sheboygan · 49,931 served
Wauwatosa Waterworks
Wauwatosa · 49,064 served
Fond Du Lac Waterworks
Fond Du Lac · 44,303 served
City of Beloit
Beloit · 36,677 served
How Nitrate Gets Into Drinking Water
Agricultural fertilizer and manure runoff
Nitrogen-based fertilizers and animal waste applied to Wisconsin cropland can leach into groundwater or run off into surface water supplies. This is the dominant nitrate pathway in most agricultural regions.
Septic system effluent
Failing or poorly sited septic systems release nitrogen-rich wastewater near drinking water wells. Rural areas with high well density and aging septic infrastructure face elevated risk.
Concentrated animal feeding operations (CAFOs)
Large livestock facilities generate significant waste. Lagoon leaks and overapplication of manure to nearby fields can create localized nitrate hotspots in groundwater.
Natural geological deposits
In some regions, naturally occurring nitrogen compounds in soil and bedrock contribute background nitrate levels to groundwater independent of agricultural activity.
Who Should Pay Closest Attention
Private well users in Wisconsin's dairy counties — particularly Kewaunee, Brown, Manitowoc, and northeastern Wisconsin — should test for nitrate and bacteria annually. Central Sands private well users should also test given documented nitrate from potato irrigation. Households with infants should prioritize current test results.
Households with infants under six months
Pregnant residents
Private well owners in agricultural areas
Households near livestock operations or CAFOs
Rural residents on shallow groundwater wells
Households with older or failing septic systems nearby
How to Check Your Situation in Wisconsin
- 1
Identify your water utility. Use the ZIP lookup below or browse the Wisconsin utility directory on this site.
- 2
Read your utility's page on this site to see its current risk level and any open nitrate violations.
- 3
Review your utility's most recent Consumer Confidence Report (CCR) — mailed annually or available on the utility's website. It must disclose any MCL exceedances.
- 4
If you are on a private well, arrange testing at a Wisconsin Department of Natural Resources (WDNR)-certified lab. Your state health department maintains a list of certified labs. Annual testing is recommended in agricultural areas.
- 5
If you have an infant under six months, use bottled water or a certified RO system (NSF/ANSI 58) immediately as a precautionary measure — do not wait for test results if you are in a high-risk area.
- 6
If your utility issues a nitrate exceedance notice, follow their guidance and do not use tap water for infants until the issue is resolved.
Treatment Options
Carbon filters and boiling do not remove nitrate. Only the options below are effective.
NSF/ANSI Standard 58 — Reverse Osmosis
RO systems certified to NSF/ANSI 58 reduce nitrate by 85–95% at the point of use. Under-sink installation required. The most practical residential option for nitrate concerns.
Distillation
Distillation units effectively remove nitrate along with most other dissolved contaminants. Suitable for drinking and cooking water — not whole-house use.
Anion Exchange
Ion exchange systems designed for nitrate removal exchange nitrate ions for chloride on a resin bed. Effective as a point-of-entry system; requires periodic regeneration and monitoring.
Carbon filters do NOT remove nitrate
Standard pitcher filters, faucet filters, and under-sink carbon units — including those certified NSF/ANSI 42 or 53 — do not remove nitrate. Do not use these for nitrate reduction.
Frequently Asked Questions
Related Pages
Nitrate — National Overview
All U.S. utilities with nitrate records
Wisconsin State Overview
All utilities and water quality data
Lead in Drinking Water
A separate but common concern
Reverse Osmosis Guide
Removes 85–95% of nitrate
Well Water Guide
Private well testing and safety
All Contaminants
Complete reference library
Data Sources & Provenance
All data on this page is sourced from official U.S. government or public datasets.
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Wisconsin Department of Natural Resources (WDNR) ↗