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Water AwarenessFoundation
All contaminants
agricultural· NO₃⁻

Nitrate

Fertilizer and animal waste runoff. Acutely dangerous for infants under 6 months.

Federal legal limit (MCL)
MCL: 10 mg/L as nitrogen
Federal health goal
MCLG: 10 mg/L
EWG health guideline
0.14 ppm
What it is

The science, plainly.

Nitrate is a nitrogen compound that enters water from agricultural fertilizer, livestock manure, and septic systems. It is the most common groundwater contaminant in U.S. farm country. Unlike most contaminants, the acute risk is the larger story: high nitrate levels can cause methemoglobinemia ('blue baby syndrome') in infants under 6 months, in which hemoglobin is rendered unable to carry oxygen.

Where it comes from

The pathways into the tap.

  • Agricultural fertilizer runoff
  • Concentrated animal feeding operations (CAFOs)
  • Septic system discharge
  • Atmospheric deposition (from combustion)
Health effects

What the evidence shows.

Acutely dangerous for infants under 6 months at levels above 10 mg/L. Longer-term, growing evidence links chronic exposure to colorectal cancer, thyroid disease, and adverse pregnancy outcomes — and some research suggests these effects may occur at levels below the EPA MCL.

Infants

Methemoglobinemia ('blue baby syndrome') — life-threatening at high doses. Never use unfiltered tap water with detectable nitrate to mix infant formula in agricultural regions.

Cancer

Multiple cohort studies associate chronic nitrate exposure (often at sub-MCL levels) with colorectal, bladder, and ovarian cancer risk.

Pregnancy

Associated with neural tube defects and other adverse birth outcomes.

Regulation

What the law allows vs. what's actually safe.

Federal legal limit (MCL)
MCL: 10 mg/L as nitrogen
Federal health goal (MCLG)
MCLG: 10 mg/L
EWG health guideline
0.14 ppm

EWG health guideline of 0.14 mg/L reflects emerging cancer-risk evidence.

Regions most affected

Where exposure is highest.

Highest in the Corn Belt (Iowa, Nebraska, Minnesota, Illinois) and the Central Valley of California. Private wells in farm country are the highest-risk source.

How to remove it

Filtration that actually works.

Effective filtration
  • Reverse osmosis
  • Anion exchange
  • Distillation
  • Note: boiling concentrates nitrate, it does not remove it

We don't recommend brands. The certification on the box matters more than the brand printed on it. Look for the actual NSF/ANSI standard number specific to the contaminant you're removing.

Check your tap

Is nitrate a problem at your address?

Enter your ZIP and we'll pull every contaminant your utility has reported — measured against EWG's health-protective guidelines.

Sources

  1. National Primary Drinking Water Regulations — U.S. Environmental Protection Agency