Important: If your well hasn’t been tested for nitrates and you’re preparing infant formula or feeding a child under 6 months, use certified bottled water or a point-of-use RO filter until you have test results. Nitrates above 10 mg/L can cause methemoglobinemia (blue baby syndrome) in infants. Bluish skin, rapid breathing, or unusual fatigue in a young infant after formula feeding is a medical emergency. Call 911 immediately.
Nitrates don’t smell, don’t taste different, and don’t change water’s appearance. You can’t detect them without a test. In agricultural areas of the Midwest, that makes them one of the most underestimated well water risks in the country.
Why the Midwest Has This Problem
Corn and soybean farming across Iowa, Illinois, Indiana, Nebraska, and Kansas requires substantial nitrogen fertilizer input. When it rains or when fields are irrigated, excess nitrogen that wasn’t taken up by crops dissolves into water and moves downward through the soil profile into groundwater.
The geology in much of the Corn Belt accelerates this. Flat terrain means water doesn’t run off, it infiltrates. Many agricultural areas have permeable soils, sometimes over fractured limestone, that allow rapid movement of surface water to groundwater. Tile drainage systems, installed under farm fields to remove standing water, create a direct conduit from surface to shallow aquifer.
The result: in heavily farmed counties, private wells draw from aquifers that have been receiving nitrate-laden water for decades. The problem isn’t new, but it’s persistent and in some areas it’s getting worse.
What the Data Shows
The USGS National Water Quality Assessment program has been monitoring groundwater quality in agricultural areas since the early 1990s. Their data consistently shows nitrate above the EPA MCL of 10 mg/L in roughly 20% of private wells in Corn Belt agricultural areas. In some counties with the highest farming intensity, exceedance rates exceed 30%.
A 2021 USGS study specifically found that shallow aquifers in the Midwest, particularly those less than 100 feet deep, had much higher nitrate concentrations than deeper aquifers. Well depth matters: older, shallower wells in agricultural areas are more vulnerable than deeper drilled wells.
Municipal water systems in the Corn Belt also deal with nitrates. The Des Moines Water Works has operated a $4.1 million nitrate removal facility for decades, one of the largest in the US, treating water from the Des Moines and Raccoon rivers before distribution. This is infrastructure that exists solely because agricultural runoff has made nitrate removal a routine necessity.
Where It’s Worst
These specific areas carry the highest documented risk based on USGS data and state monitoring:
Iowa: Sioux County, Buena Vista County, Crawford County, Shelby County. These are high-density row crop farming counties with shallow aquifers.
Illinois: McLean County, Livingston County, Iroquois County. Flat terrain, intensive farming, tile drainage throughout.
Indiana: Whitley County, Kosciusko County, and surrounding north-central counties. Sandy glacial outwash aquifers with high permeability.
Nebraska: Platte River Valley (Platte County, Butler County, Colfax County), York County, Seward County. Heavy irrigated corn and soybean production over the Platte aquifer system.
Kansas: South-central counties along the Arkansas River basin. Irrigated wheat and sorghum production areas.
This isn’t a complete list. If you live in an agricultural county in any of these states and have a private well, treat it as potentially at risk until you test.
Why Boiling Makes It Worse
This point gets missed often enough that it’s worth stating plainly: boiling water to make it “safer” concentrates nitrates. As water evaporates during boiling, the nitrates stay in the remaining water at a higher concentration per unit volume.
Never boil water to reduce nitrates. It does the opposite.
The same logic applies to long cooking times that reduce volume. Reconstituting infant formula with water that has been simmered down, even slightly, increases nitrate concentration.
Who Is Most at Risk
Infants under 6 months face the most acute risk. The mechanism is specific: infants have gut bacteria that reduce nitrates to nitrites more efficiently than adults, and infant hemoglobin is more susceptible to conversion to methemoglobin. Methemoglobin can’t carry oxygen. At high enough methemoglobin levels, an infant can’t get enough oxygen to the brain and organs.
Blue baby syndrome is not a historical rarity. Cases still occur when well water with elevated nitrates is used for formula. The CDC and EPA maintain the 10 mg/L MCL specifically to protect infants.
For adults: the acute health risk from nitrates is much lower. Long-term elevated exposure has been associated with colorectal cancer risk in some studies, including a large prospective study published in the International Journal of Epidemiology (Ward et al., 2010). The association is real but causation isn’t firmly established. It’s a reason to take elevated nitrates seriously for the whole household, not just for infants.
Pregnant women and people with certain health conditions that affect blood oxygen are also in a higher-risk group.
Treatment That Works
Reverse osmosis certified to NSF/ANSI 58 removes 70-90% of nitrates. This is point-of-use treatment at the kitchen tap and is the most common household solution.
Ion exchange with an anion resin removes nitrates specifically. This can be configured as whole-house treatment, which matters for households using well water for all cooking, not just for water poured from a tap.
Distillation removes nitrates as well, though home distillers are less common.
Standard activated carbon filters, including Brita, PUR, and most pitcher filters, do not remove nitrates. NSF certification listing for contaminant removal doesn’t include nitrates for standard carbon. Confirm any filter’s nitrate removal claim against the manufacturer’s NSF certificate before relying on it.
See our reverse osmosis system reviews and our mail-in water test reviews for specific product recommendations.
Testing: When and How Often
Annual testing is the baseline recommendation for private wells in agricultural areas. Spring is the highest-risk season, after snowmelt and spring rains have flushed nitrogen through the soil profile. If you’re going to test once, test in April or May.
Also test after any significant flooding. Floodwater carries surface contaminants directly into wells, and post-flood nitrate spikes are well-documented.
A nitrate test from a certified lab costs $10-20 on its own. A basic well water panel that includes nitrates, bacteria, hardness, and pH runs $75-150 at most certified labs. Your state health department can refer you to a certified lab. See our well water testing guide for the full process.
The full nitrates contaminant page has more detail on the health science and treatment options.