Nitrite is a nitrogen-containing chemical that can occur naturally in the environment but is more commonly associated with fertilizer runoff, wastewater, septic systems, animal waste, and the biological conversion of nitrogen compounds.

Although nitrite and nitrate are closely related, they are not the same chemical. Both are regulated in drinking water because elevated concentrations can interfere with the blood’s ability to transport oxygen. Infants are particularly vulnerable to this effect. (US EPA)

Nitrite can be especially important for people who rely on private wells, particularly wells near agricultural areas or septic systems.

This guide explains what nitrite is, potential health risks, EPA drinking-water standards, how to test for nitrite, the best treatment methods, and what homeowners should look for when choosing a water filtration system.

For a broader look at contaminants that can affect drinking water, see RevOsmo’s Drinking Water Contaminants Explained.

What Is Nitrite?

Nitrite (NO₂⁻) is a nitrogen-oxygen compound that is part of the natural nitrogen cycle.

Nitrite can form when bacteria convert ammonia into nitrite or when nitrate is reduced under certain environmental conditions. It can subsequently be converted into nitrate or other nitrogen compounds.

Nitrite can enter drinking-water sources from:

Agricultural fertilizer
Animal manure
Septic systems
Sewage
Wastewater
Runoff
Industrial activities
Naturally occurring nitrogen compounds
Nitrification within some water-distribution systems

EPA identifies nitrate and nitrite as nitrogen-oxygen compounds and notes that fertilizer use and wastewater-related sources can contribute to their presence in drinking water. (US EPA)

Nitrite vs. Nitrate: What’s the Difference?

Nitrite and nitrate are closely related but have different chemical formulas.

Contaminant	Formula	EPA MCL
Nitrate, measured as nitrogen	NO₃⁻	10 mg/L
Nitrite, measured as nitrogen	NO₂⁻	1 mg/L

Both federal standards are expressed as nitrogen (N), which is important when interpreting laboratory results. (US EPA)

Nitrate can also be converted to nitrite inside the body. EPA explains that this conversion can interfere with the blood’s oxygen-carrying capacity. (US EPA)

How Does Nitrite Get Into Drinking Water?

There are several potential pathways.

Agricultural Fertilizer

Nitrogen fertilizers applied to agricultural land can contribute nitrogen compounds to groundwater and surface water.

Rain and irrigation can move nitrogen compounds through soil and into groundwater.

Animal Waste

Manure and animal waste can be significant sources of nitrogen contamination.

This can be particularly important for private wells located near:

Farms
Livestock operations
Manure storage
Agricultural fields

Septic Systems

Poorly maintained or failing septic systems can release nitrogen compounds into groundwater.

A private well located too close to a septic system can be particularly vulnerable.

Sewage and Wastewater

Wastewater can contain nitrogen compounds that eventually reach surface water or groundwater.

Distribution-System Nitrification

Nitrite can also form within some drinking-water distribution systems through nitrification, particularly in systems that use chloramines as a secondary disinfectant.

EPA identifies nitrification in distribution systems as an important source of nitrate and nitrite formation. (US EPA)

Health Risks of Nitrite in Drinking Water

The most important health concern associated with elevated nitrite exposure is its effect on the blood’s ability to carry oxygen.

Nitrite can contribute to the formation of methemoglobin, a form of hemoglobin that does not transport oxygen effectively.

Blue Baby Syndrome

Infants are particularly vulnerable.

High levels of nitrate or nitrite can cause methemoglobinemia, commonly called blue baby syndrome.

Symptoms can include:

Shortness of breath
Bluish skin
Fatigue
Weakness
Rapid heart rate

Severe cases can become life-threatening.

EPA states that infants below six months who consume water containing nitrite above the federal MCL can become seriously ill and, if untreated, may die. (EPA)

This is why nitrate and nitrite contamination deserves particular attention in households with infants.

Who Is Most Vulnerable?

The most important sensitive population is infants, particularly those younger than six months.

EPA’s drinking-water risk framework specifically considers sensitive populations when establishing public-health goals and standards. (US EPA)

Households should be especially cautious when:

Preparing infant formula
Using untreated private-well water
Living near agricultural operations
Living near septic systems
A well has previously tested positive for nitrate or nitrite

If a water test indicates elevated nitrite, follow the recommendations of your local health department or water professional before using the water for infant consumption or formula preparation.

EPA Guidelines for Nitrite in Drinking Water

Nitrite is a regulated drinking-water contaminant under the federal Safe Drinking Water Act framework.

EPA’s current standard is:

Nitrite MCL: 1 mg/L as nitrogen

That’s equivalent to approximately:

1 part per million (ppm) as nitrogen.

EPA lists an MCL of 1 mg/L for nitrite measured as nitrogen. (US EPA)

For comparison:

Nitrate MCL: 10 mg/L as nitrogen

These are separate federal standards.

What Does the EPA Nitrite Limit Mean?

The Maximum Contaminant Level (MCL) is a legally enforceable standard applicable to public water systems.

It is not simply a recommended “ideal” concentration.

EPA explains that National Primary Drinking Water Regulations establish legally enforceable standards designed to protect public health. (US EPA)

Importantly, the federal nitrite MCL applies to public water systems. Private wells are not regulated in the same manner under the federal Safe Drinking Water Act.

Nitrite and Private Well Water

If you rely on a private well, you are responsible for testing your water.

The CDC recommends annual testing of private wells for nitrate and coliform bacteria, and additional testing may be appropriate based on local conditions. (CDC Stacks)

Consider testing more frequently if:

Your well has flooded
You have a new baby
You live near agricultural fields
Fertilizer is used nearby
Your septic system has problems
Your well has been damaged
Nearby wells have nitrate or nitrite contamination
Water quality has changed

How to Test for Nitrite in Drinking Water

Testing for nitrite requires a water-quality laboratory or appropriate analytical test.

When ordering a laboratory test, pay close attention to how the result is reported.

A laboratory may report:

Nitrite as nitrogen (NO₂-N)

or may report nitrite as the entire chemical ion.

These measurements are not interchangeable.

Always compare your result with the EPA standard using the same units.

The federal MCL is:

1 mg/L as nitrogen (NO₂-N). (US EPA)

Should You Test for Nitrate and Nitrite Together?

Yes.

Because nitrate and nitrite are closely related and can both occur as a result of nitrogen contamination, testing for both is generally more informative than testing for nitrite alone.

A comprehensive private-well water test may also include:

Total coliform
E. coli
pH
Total dissolved solids
Nitrate
Nitrite

The CDC specifically recommends annual nitrate and coliform testing for private wells. (CDC Stacks)

What Causes High Nitrite in Well Water?

High nitrite may be associated with:

Agricultural runoff
Fertilizer
Animal waste
Septic-system leakage
Sewage contamination
Poor well construction
Flooding
Local groundwater conditions

The exact source should be investigated rather than assuming that a filtration system alone solves the problem.

Best Filtration Methods for Nitrite

Nitrite is a dissolved inorganic ion, so basic sediment filtration isn’t an appropriate treatment.

The most relevant residential treatment technologies include:

Reverse osmosis
Anion exchange
Distillation
Specialized ion-exchange treatment

1. Reverse Osmosis

Reverse osmosis (RO) is one of the most practical point-of-use options for reducing nitrite and nitrate.

RO uses pressure to force water through a semipermeable membrane.

The membrane can reject many dissolved inorganic contaminants.

EPA identifies reverse osmosis and nanofiltration as membrane treatment processes capable of removing a wide range of contaminants. (US EPA)

For homeowners, an under-sink RO system can provide treated water for:

Drinking
Cooking
Coffee
Tea
Ice
Infant formula preparation

When selecting an RO system, verify the manufacturer’s performance information for nitrate/nitrite specifically.

2. Anion Exchange

Anion exchange is another important technology for nitrate and nitrite treatment.

During the process, negatively charged contaminants are exchanged with other negatively charged ions on a specialized resin.

EPA identifies anion exchange as a treatment technology useful for negatively charged contaminants including nitrate. (US EPA)

A properly selected ion-exchange system can be effective, but performance depends on:

Resin type
Water chemistry
Flow rate
Contaminant concentration
Competing ions
Resin capacity
Maintenance

3. Distillation

Distillation heats water to produce steam and then condenses that steam into treated water.

Because many dissolved minerals and inorganic contaminants do not readily transfer with the steam, distillation can reduce a range of dissolved contaminants.

EPA specifically identifies distillation as a treatment option for water with elevated nitrate. (US EPA)

However, distillation can be:

Energy intensive
Slow
More expensive to operate
Less convenient for treating large volumes

4. Whole-House Treatment

Whole-house treatment may be appropriate when nitrite contamination is present throughout a private well.

However, if the primary concern is drinking and cooking water, point-of-use treatment may be more practical.

An under-sink RO system can provide treated water directly at the kitchen faucet without treating every gallon used for:

Showers
Laundry
Toilets
Outdoor irrigation

The appropriate choice depends on the contamination level and household needs.

Does a Carbon Filter Remove Nitrite?

A standard activated-carbon filter should not be considered a reliable treatment for nitrite.

Carbon filtration is excellent for many organic chemicals, chlorine, and taste/odor compounds, but nitrite is an inorganic negatively charged ion.

For elevated nitrite, consider treatment technologies specifically designed for dissolved inorganic contaminants, particularly reverse osmosis or anion exchange.

Does a Water Softener Remove Nitrite?

No—not reliably.

Water softeners are primarily designed to reduce hardness caused by:

Calcium
Magnesium

They should not be considered a dedicated nitrite-removal system.

Does Reverse Osmosis Remove Nitrite?

Reverse osmosis can reduce nitrite and nitrate, making it one of the most practical household treatment options.

However, actual performance depends on:

Membrane type
System design
Feed-water chemistry
Pressure
Flow rate
Membrane condition
Filter maintenance

EPA identifies RO as a treatment technology for a broad range of dissolved contaminants. (US EPA)

When purchasing a system, look for product documentation specifically addressing nitrate/nitrite reduction.

Does Boiling Remove Nitrite?

No. Boiling should not be used as a solution for nitrite contamination.

Boiling is useful for killing microorganisms, but it does not reliably remove dissolved nitrate or nitrite.

In fact, boiling water can concentrate nonvolatile dissolved substances as water evaporates.

If nitrite exceeds the applicable limit, use a safe alternative water source and/or an appropriate treatment system.

Best Water Filter for Nitrite

For most homeowners, the most practical options are:

Best Point-of-Use Option

Reverse osmosis

Best Specialized Treatment

Anion exchange

Alternative Treatment

Distillation

The best option depends on the concentration, water chemistry, household water demand, and whether treatment is needed at one faucet or throughout the home.

What to Do If Your Water Tests High for Nitrite

If laboratory testing shows elevated nitrite:

1. Don’t Ignore the Result

Nitrite is regulated because elevated levels can present a serious health concern, particularly for infants.

2. Confirm the Units

Make sure the result is reported in the same units as the EPA standard—mg/L as nitrogen.

3. Consider Retesting

If the result is unexpected, confirm it through a qualified laboratory.

4. Identify the Source

Investigate potential sources such as:

Septic systems
Fertilizer
Agricultural activity
Animal waste
Flooding
Well construction

5. Use an Alternative Water Source When Appropriate

EPA recommends a safe alternative drinking-water source when regulated nitrate levels are exceeded and treatment has not yet been implemented. (US EPA)

6. Install Appropriate Treatment

RO or anion exchange may be appropriate depending on the situation.

7. Retest After Treatment

Always verify that the treatment system is actually reducing the contaminant to an acceptable level.

Nitrite and Infant Formula

This is an especially important consideration for households with infants.

Because elevated nitrate and nitrite can interfere with oxygen transport in infants, parents should be particularly careful about using untreated private-well water for infant formula.

If a private well has elevated nitrate or nitrite, consult local public-health or water-quality authorities about an appropriate safe water source.

EPA specifically identifies infants as the population at greatest concern for nitrate/nitrite exposure. (US EPA)

Frequently Asked Questions

What is nitrite in drinking water?

Nitrite is a nitrogen-oxygen compound that can enter water from fertilizer, animal waste, septic systems, wastewater, and other nitrogen sources.

Is nitrite dangerous in drinking water?

Elevated nitrite can interfere with the blood’s ability to transport oxygen. Infants are particularly vulnerable, and severe exposure can cause methemoglobinemia or “blue baby syndrome.” (US EPA)

What is the EPA limit for nitrite?

EPA’s federal MCL is 1 mg/L (1 ppm) measured as nitrogen. (US EPA)

What is the difference between nitrate and nitrite?

Nitrate is NO₃⁻, while nitrite is NO₂⁻. Both are nitrogen-containing compounds, and nitrate can be converted to nitrite in the body. (US EPA)

Does reverse osmosis remove nitrite?

RO can reduce nitrite and nitrate and is one of the practical household treatment options. Actual performance varies by system and water chemistry. (US EPA)

Does activated carbon remove nitrite?

Standard activated-carbon filters should not be relied upon as a primary treatment for elevated nitrite.

Does boiling remove nitrite?

No. Boiling does not provide a reliable way to remove dissolved nitrite.

Does a water softener remove nitrite?

No. Water softeners are designed primarily to reduce hardness minerals and should not be relied upon for nitrite removal.

Should private-well owners test for nitrite?

Testing for nitrate and nitrite can be appropriate, particularly for wells near agricultural activity, septic systems, or known contamination. Annual testing for nitrate and coliform bacteria is recommended for private wells by CDC guidance. (CDC Stacks)

Final Thoughts

Nitrite is an important drinking-water contaminant because elevated concentrations can interfere with the body’s ability to transport oxygen.

The greatest concern is for young infants, particularly those under six months of age. EPA’s federal drinking-water standard for nitrite is 1 mg/L as nitrogen. (US EPA)

If you rely on a private well, regular testing is one of the best ways to identify nitrate and nitrite problems before they become a larger concern.

If nitrite is detected at elevated levels:

Confirm the laboratory result and units.
Test for nitrate as well.
Investigate potential contamination sources.
Use a safe alternative drinking-water source when appropriate.
Consider reverse osmosis or anion-exchange treatment.
Verify treatment performance through follow-up testing.

For the broader RevOsmo resource covering contaminants such as nitrite, nitrate, PFAS, lead, arsenic, fluoride, pesticides, and other drinking-water concerns, visit Drinking Water Contaminants Explained.

If you’re ready to compare treatment systems, visit Best Reverse Osmosis Systems for Home, Best Under Sink Water Filters, and Water Filter Reviews.

Disclaimer: This article is for educational purposes and is not medical, regulatory, or professional water-treatment advice. EPA standards and public-health guidance can change. If laboratory testing indicates elevated nitrite—especially in a household with an infant—consult your local health department, water utility, or qualified water-treatment professional before relying on the water for drinking or formula preparation.