Guide · Updated October 14, 2026

Nitrates in Wisconsin Well Water

Nitrate does not rust a sink. It does not color the glass. You cannot taste, smell, or see it. The only number that counts is a certified-lab result in mg/L as nitrogen (nitrate-N). Until that sheet is in your hand, a county average, a neighbor’s well, or a treatment catalog is not a diagnosis.

Wisconsin private wells are not regulated like a municipal system. The Safe Drinking Water Act does not cover private wells; testing and treatment are the owner’s job. DNR’s annual private-well page and DHS’s private-wells page both put bacteria and nitrate on that list. Nobody mails you a Consumer Confidence Report.

This page is a reading order for that sheet — not a medical consult and not a shopping list. EPA and Wisconsin DHS publish infant- and pregnancy-related language on their nitrate pages. This site does not reprint that list as a diagnosis and will not turn a mg/L into a personal risk score. If the number is high or the units are unclear, take the sheet to the local health department.

If you are on a city or utility system, look up that system’s Consumer Confidence Report through your water provider or Wisconsin DNR drinking water. That report is not a private-well sheet.

What 10 mg/L as N means — and what it is not

EPA’s National Primary Drinking Water Regulations table lists nitrate measured as nitrogen with an MCL of 10 mg/L. That is the same magnitude as 10 ppm. Nitrite as nitrogen is a different line (1 mg/L). A nitrate number is not a nitrite number. EPA lists the public-system health concern as methemoglobinemia (“blue baby syndrome”) in infants under six months. This page does not turn that sentence into a household diagnosis.

That MCL is a Safe Drinking Water Act limit for public systems. Private wells are not under that Act. Do not call 10 mg/L as N a kitchen-tap legal limit. It is the comparison number DNR, DHS, and EPA already use.

Units. Ask the lab whether the sheet is as N or as NO₃. Those are not interchangeable. Ten milligrams per liter as nitrogen is the MCL. Ten milligrams per liter as nitrate ion is about 44 mg/L as NO₃. If your sheet says 30 mg/L and does not say which, ask the lab. If the reporting limit sits at or above 10 mg/L as N, you bought a test that cannot tell you whether you are under the line. How to read a well water lab report is the decoder.

Wisconsin DHS uses the same 10 mg/L nitrate-nitrogen line for private wells: at or above that level, stop using the water for infant formula and for anyone who is or may become pregnant until you have another source or treatment. Talk to a doctor about any result near the limit — not this directory.

Why Wisconsin wells pick up nitrate

Nitrate in groundwater usually traces back to:

• Fertilizer and manure on cropland, pasture, and around livestock operations — a common pathway in Wisconsin’s dairy and cash-crop counties.
• Septic systems too close to the well or failing.
• Poor well construction — a missing sanitary seal, a cracked casing, a wellhead in a low spot where runoff ponds.
• Shallow wells in permeable aquifers, especially in karst or sandy soils where surface water reaches the water table quickly.

Wisconsin DNR and DHS both note that agricultural nitrogen and septic systems are common private-well nitrate sources statewide. A neighbor’s clean result or a county average does not describe your well. Only a sample from your tap does. This page will not invent a Wisconsin occurrence percent.

The Minnesota nitrates, Iowa nitrates, and Texas nitrates pages are the peer-state versions of the same split: a map is not a kitchen tap.

How often to test

Wisconsin DNR and DHS recommend testing a private well at least once a year for bacteria and nitrate, and testing nitrate again before the water will be used by someone who is or may become pregnant or to prepare infant formula. Test sooner after a flood, a nearby septic or fertilizer change, or a change in taste, color, or smell. CDC’s annual backbone is the same pair — coliform and nitrate — plus total dissolved solids and pH.

DNR’s Nitrate in Drinking Water (DG-001) also notes that wells between 5 and 10 mg/L as N should be retested annually, and that a nitrate test is recommended for newly constructed wells.

Bacteria on the same sheet still goes to the health department first. Do not shop a nitrate stage while coliform is open.

Get a certified-lab mg/L as N — not a store-kit guess

Start at this site’s Wisconsin certified-lab inventory. Chemistry certification is DNR; bacteria certification is DATCP. A wastewater certificate is not a drinking-water nitrate certificate.

Open DNR’s certified laboratory lists and the private-well testing page. Confirm nitrate on the current drinking-water chemistry list. Then call: private-well / residential sample, bottle, hold time. Bacteria bottles must reach the lab within 48 hours on DNR’s published line. Nationwide index: certified labs by state. Lab news: /labs/wisconsin/news. Sibling page: Arsenic in Wisconsin Well Water.

Certified paths include a local or tribal health department, the Wisconsin State Laboratory of Hygiene, a University of Wisconsin lab, or a commercial lab. Households with pregnant people and young children may be eligible for no-cost testing through WellTAP or the local health department — ask before you pay.

If your well has a Unique Well Number, include it when the lab asks. WSLH results are reported to DNR for filing.

Sample the cooking and drinking tap. Untreated: usually kitchen cold. Treated: after the tank, unless the lab says otherwise. Use the lab’s bottle. Run the cold tap a few minutes first. Ship within the hold time.

A store strip is a screen. Official first: DNR certified-lab lists, DATCP bacteria lists, the local health department, or WSLH (/labs/wisconsin). Tap Score / SimpleLab is a second-path mail-in kit example, not a ranked pick. Well Diagnosis may earn a commission if you buy through an approved affiliate link. See the disclosure. Confirm nitrate and coliform on the order form.

What to do with the number

Do not boil high-nitrate water. Boiling does not remove nitrate; it concentrates it as water evaporates. Use treatment or an alternative source instead.

Before buying equipment, look for the cause: wellhead grade and cap, distance to septic, fertilizer or manure storage near the well. A licensed Wisconsin well driller or pump installer can inspect construction. DNR’s Tests for Private Well Users (DG-023) is the official list of which tests to run and when. This site will not turn 10 mg/L as N into a personal risk score.

After the sheet: classes, not a catalog

Name the class after you have a mg/L as N. Then look the model up in the NSF drinking-water treatment-unit database. NSF is a claim on a listed model — often NSF/ANSI 58 for reverse osmosis — not a badge this site awards. This page does not rank brands.

Nitrate is removed by a short list of technologies, and a softener or iron filter is not one of them:

• Point-of-use reverse osmosis at the kitchen sink, certified for nitrate reduction under NSF/ANSI 58. The usual first step for drinking and formula water.
• Nitrate-selective anion exchange for whole-house treatment when levels are high throughout and a licensed installer says it fits.
• Distillation at point of use.

A water softener alone does not remove nitrate. Do not buy salt “for nitrate.” An oxidizing iron filter is the wrong class.

Check any unit against NSF for a nitrate claim and retest after install. RO membranes also need clear pretreated water; see treatment order after the pressure tank. Retest the treated tap at least yearly.

If bacteria is present, stop. Health department first. A nitrate cartridge on a contaminated well is the wrong Monday.

Bottom line

A Wisconsin private well with an unknown nitrate level is a question, not a crisis. Order a certified-lab nitrate test from the Wisconsin inventory. Compare mg/L as N to EPA’s public-system MCL of 10 — as a teaching number, not a private-well legal limit. At or above 10, call the health department, keep infants and pregnancy off the tap, and do not boil. Treatment class comes after the sheet. A softener is the wrong class. Bacteria still goes to the health department.

Updated 2026-09-27.