Nitrates in Drinking Water

Data source: U.S. EPA, CDC

What Are Nitrates?

Nitrates (NO₃⁻) are naturally occurring compounds in the nitrogen cycle, but they appear in drinking water at elevated levels primarily due to human activity. They are colorless, odorless, and tasteless — meaning contaminated water looks and tastes completely normal. Nitrates are measured as nitrogen (mg/L as N) in EPA regulations.

Health Effects

Nitrates are of greatest concern for infants under 6 months of age:

• Methemoglobinemia ("blue baby syndrome") — nitrates interfere with blood oxygen transport; in severe cases, infants may turn bluish and can suffer brain damage or death
• Thyroid effects — chronic exposure may disrupt thyroid hormone production in adults
• Potential cancer associations — some studies link long-term high nitrate intake to colorectal and other cancers, though evidence is still developing
• Pregnancy concerns — elevated exposure may be associated with adverse birth outcomes

Healthy adults can generally tolerate nitrate levels at or below the MCL, but infants, pregnant women, and immunocompromised individuals are at greater risk.

How Nitrates Get Into Water

Nitrates enter groundwater and surface water through multiple pathways:

• Agricultural runoff — nitrogen-based fertilizers applied to crops leach through soil into aquifers; the single largest source in rural areas
• Animal waste — livestock operations generate high concentrations of nitrogen compounds
• Septic systems — improperly maintained or failing septic systems release nitrates into surrounding soil and groundwater
• Natural sources — some geological formations contain elevated natural nitrate levels

Nitrate contamination is highest in the Corn Belt (Iowa, Illinois, Indiana, Nebraska), the Central Valley of California, and regions with dense livestock operations.

EPA Standards

The EPA Maximum Contaminant Level (MCL) for nitrates is 10 mg/L as nitrogen. A separate MCL for nitrites (NO₂⁻) is 1 mg/L as nitrogen, with a combined nitrate + nitrite limit of 10 mg/L.

Nitrate is one of the most commonly violated MCLs in U.S. drinking water. Community water systems are required to monitor and report exceedances. Private well owners are not regulated and must test their own water.

How to Remove Nitrates From Drinking Water

Standard carbon filters do not remove nitrates. This is a critical point — neither activated carbon pitchers nor standard under-sink carbon filters are effective. Effective methods include:

• Reverse osmosis (RO) — removes 85–95% of nitrates; NSF 58 certified point-of-use units are widely available for under-sink installation
• Ion exchange (anion exchange resin) — highly effective for nitrate removal; used in both point-of-use and whole-house systems; look for NSF 44 or NSF 62 certification
• Distillation — removes virtually all nitrates; slow and energy-intensive but effective

If you have an infant under 6 months in the household, use only certified filtered or commercially bottled water for formula preparation when nitrate levels exceed 10 mg/L.

Nitrates in U.S. Water Systems: What the Data Shows

ZipCheckup aggregates CCR data and EPA enforcement records to track nitrate contamination across the country:

• 27 water systems serving 406 ZIP codes reported nitrate detections in their most recent Consumer Confidence Reports
• 996 EPA enforcement actions for nitrate and nitrite violations have been recorded across 210 ZIP codes
• In total, nitrate-related data affects 584 ZIP codes in our database

Nitrate is one of the most commonly violated MCLs in the U.S., particularly in agricultural regions where fertilizer runoff and livestock operations drive contamination.

Is Nitrate a Problem in Your Area?

Nitrate exceedances are disproportionately concentrated in agricultural communities and areas with dense livestock operations. Small community water systems and private wells in rural areas are at highest risk. Many violations go undetected in households relying on private wells, which are not subject to federal monitoring requirements.

ZipCheckup tracks EPA SDWIS nitrate violations by ZIP code for community water systems.