What is the EPA limit for nitrate in drinking water?

The EPA Maximum Contaminant Level (MCL) for nitrate in public drinking water is 10 mg/L (milligrams per liter), also expressed as 10 ppm (parts per million) as nitrogen. For nitrite, the MCL is 1 mg/L. The combined nitrate + nitrite MCL is also 10 mg/L. These MCLs apply to public water systems — private wells are not regulated under these rules.

Why is nitrate dangerous for infants?

Nitrate in drinking water is converted to nitrite in the body. In infants under 6 months, nitrite interferes with hemoglobin's ability to carry oxygen, causing a condition called methemoglobinemia (blue baby syndrome). Adults and older children are much less susceptible because stomach acid inhibits the bacteria that convert nitrate to nitrite. The EPA MCL of 10 mg/L is specifically designed to protect infants.

Can boiling water remove nitrate?

No. Boiling does not remove nitrate — it concentrates it. As water evaporates during boiling, the nitrate concentration in the remaining water increases. Do not use boiled water for infant formula if nitrate is a concern.

Where does nitrate in water come from?

The most common sources of nitrate in drinking water are fertilizers applied to agricultural land, animal waste (feedlots, manure), and septic systems. Nitrate leaches through soil into groundwater, where it enters private wells and sometimes public water supply sources. Areas with intensive agriculture, particularly corn-belt and livestock regions, tend to have higher nitrate levels in groundwater.

Do I need to test for nitrate if I'm on a public water system?

Public utilities are required to test for nitrate and report violations. If your utility has had nitrate exceedances, that would appear in compliance data and Consumer Confidence Reports. For public utility users, checking your utility's compliance history is the starting point. Private well users are not covered by utility monitoring and are responsible for their own testing.

What filters remove nitrate from water?

Reverse osmosis (RO) is the most effective point-of-use method for nitrate removal. Ion exchange systems (specifically anion exchange with nitrate-selective resin) are also effective. Standard activated carbon filters do not reliably remove nitrate. Distillation also removes nitrate. Look for NSF/ANSI 58 certification (RO) or NSF/ANSI 62 (distillation) for certified performance.

Water Testing Labs

Contaminant Testing Guide

Nitrate Water Testing: What Nitrate Levels Mean and How To Test

Nitrate is one of the most common contaminants in private well water in agricultural regions. The EPA maximum contaminant level of 10 mg/L is specifically set to protect infants. Boiling water does not remove nitrate — it concentrates it.

Last updated: 2026-05-13 · Source: EPA, CDC

Direct Answer

The EPA MCL for nitrate is 10 mg/L. Above this level, nitrate poses a documented health risk to infants under 6 months (methemoglobinemia). Private well users in agricultural areas are most likely to encounter elevated nitrate — annual testing is commonly recommended. Standard carbon filters do not remove nitrate; reverse osmosis and ion exchange do.

Important for households with infants under 6 months

Do not use water with nitrate above 10 mg/L for infant formula. Do not boil the water — boiling concentrates nitrate. Use bottled water or a certified reverse osmosis system while awaiting test results or if results exceed 10 mg/L.

Where Nitrate in Water Comes From

Agricultural fertilizers

Nitrogen-based fertilizers applied to cropland leach through soil into groundwater. Corn-belt states and other intensive agriculture regions show the highest nitrate levels in groundwater monitoring data.

Animal waste

Feedlots, manure lagoons, and pasture land contribute nitrate to groundwater through runoff and soil infiltration. Proximity to concentrated animal feeding operations (CAFOs) increases risk.

Septic systems

Improperly sited, failing, or overloaded septic systems can introduce nitrate into surrounding groundwater. Older septic systems in high-density areas are a documented source.

Who Should Test for Nitrate

Private well users in agricultural areas

Highest risk group; annual testing commonly recommended

Households with infants under 6 months

Infant health risk applies even at moderate levels

Households near feedlots or CAFOs

Proximity to concentrated animal operations increases groundwater nitrate

Households with older or failing septic systems

Especially if well is downgradient of the septic field

Households with shallow wells

Shallower wells are more susceptible to surface contamination

Anyone whose utility has reported nitrate violations

Check your utility's compliance history first

How To Test for Nitrate

Find a certified lab

Nitrate testing is included in most standard water panels at state-certified laboratories. Use the EPA certified lab directory or your state health department's list. Confirm nitrate (and nitrite if desired) are included.

Collect a water sample

Nitrate sampling does not require the first-draw protocol used for lead. Follow your lab's collection instructions. For well samples, collect from the tap closest to the pressure tank.

Compare results to the MCL

Results are reported in mg/L (ppm) as nitrogen. The EPA MCL is 10 mg/L. If results are near or above this level, consult your state health department and evaluate treatment options.

Nitrate Benchmarks

EPA MCL for nitrate (as N)

10 mg/L

Health-based limit for public utilities; reference for wells

EPA MCL for nitrite (as N)

1 mg/L

Separate limit for nitrite compound

Combined nitrate + nitrite MCL

10 mg/L

Total combined limit

Nitrate Treatment Options

Reverse osmosis (RO) — most common point-of-use option

RO membranes reject nitrate effectively. NSF/ANSI Standard 58 covers reverse osmosis systems for nitrate reduction. Undersink RO systems treat water at a single tap. Effective for both nitrate and nitrite.

Ion exchange (anion exchange with nitrate-selective resin)

Anion exchange systems are effective for nitrate removal. Standard water softeners (cation exchange) do not remove nitrate. Systems must use nitrate-selective resin, not general-purpose softener resin.

Distillation

Distillation removes nitrate. NSF/ANSI 62 certifies distillation units. Distillers are generally slower and higher-maintenance than RO systems for residential use.

Activated carbon filters — not effective for nitrate

Standard carbon block or GAC filters do not reliably remove nitrate. Do not rely on a carbon filter for nitrate removal.

Next Steps

Find a certified water testing lab

State-certified and NELAP-accredited labs

Nitrate contaminant guide

Health context, EPA limits, and geographic prevalence

Well water testing guide

Nitrate is a baseline test for private well users

Reverse osmosis treatment guide

How RO removes nitrate and other contaminants

What to test for in drinking water

Full guide by contaminant and situation

How to read water test results

Interpreting mg/L and ppm in lab reports

Nitrate Water Testing FAQs

Data Sources and Methodology

Nitrate guidance is drawn from EPA National Primary Drinking Water Regulations, EPA health advisories, CDC methemoglobinemia guidance, and USGS groundwater quality research. Full methodology →

EPA Nitrate MCL CDC Methemoglobinemia USGS Nitrate in Groundwater

Last updated: 2026-05-13