Ammonium in water: origin, risks, standards, and treatment

Ammonium is a dissolved form of nitrogen resulting from the decomposition of organic matter, wastewater, agricultural runoff, or certain geological conditions. Its presence does not generally cause direct toxicity at typical concentrations, but it can interfere with disinfection, promote bacterial growth, and be converted into nitrites and then nitrates. In the European Union, ammonium is an indicator parameter set at 0.50 mg/L.

Formula: NH₄⁺
Associated equilibrium: NH₃/NH₄⁺
Main risk: Nitrification
EU value: 0.50 mg/L

What is ammonium?

Ammonium is an ion with the formula NH₄⁺. It forms when dissolved ammonia NH₃ captures a proton in water. Both forms coexist in an equilibrium primarily controlled by pH and temperature.

In most natural waters near neutrality, the ammonium form is largely dominant. As pH and temperature increase, the proportion of non-ionized ammonia rises. This distinction is important because free ammonia is more volatile, more reactive, and more toxic to aquatic organisms.

In drinking water, ammonium is primarily considered a quality and treatment process indicator. A high concentration can reveal recent pollution, decomposition of organic matter, contamination by wastewater, a specific geological origin, or insufficiently controlled nitrification.

Key takeaway: Ammonium is generally not regulated for direct toxicity at typical drinking water concentrations, but rather for its effects on treatment, disinfection, taste, networks, and the potential formation of nitrites and nitrates.

Ammonia, ammonium, and ammoniacal nitrogen

The term "ammoniacal nitrogen" often refers to the sum of ammonia NH₃ and ammonium NH₄⁺, expressed as the mass of nitrogen. Results may therefore appear in different forms depending on the laboratory and regulations.

Term	Formula	Main characteristic
Non-ionized ammonia	NH₃	More volatile form, favored by high pH and temperature.
Ammonium	NH₄⁺	Ionized form dominant in most drinking waters.
Ammoniacal nitrogen	NH₃-N + NH₄-N	Analytical expression based on the mass of nitrogen.
Total ammonia	Sum of ammoniacal species	The exact definition must be verified in the analysis report.

At a pH near 7 and room temperature, ammonium accounts for the vast majority of ammoniacal nitrogen. At a higher pH, the NH₃ fraction increases rapidly. The relationship between the two forms is reversible and does not constitute an irreversible transformation.

How do pH and temperature influence the equilibrium?

The equilibrium can be simplified by the following reaction: NH₄⁺ ⇌ NH₃ + H⁺.

a low pH favors ammonium NH₄⁺;
a high pH favors ammonia NH₃;
a higher temperature generally increases the non-ionized fraction;
aquatic toxicity increases as the NH₃ fraction increases.

To interpret an environmental analysis, the total concentration is therefore not always sufficient. pH and temperature must be known to estimate the non-ionized ammonia fraction.

What is the role of ammonium in the nitrogen cycle?

Ammonium is a central form in the nitrogen cycle. It is produced during the decomposition of nitrogen-containing organic matter, a process called ammonification.

Ammonification

Proteins, amino acids, urea, and other nitrogenous compounds are broken down by microorganisms, releasing ammonium.

Nitrification

In the presence of oxygen, specialized microorganisms oxidize ammonium to nitrite, and then nitrite to nitrate. This reaction consumes oxygen and alkalinity.

Assimilation

Plants, algae, and microorganisms can absorb ammonium as a nitrogen source to produce organic matter.

Denitrification

After transformation into nitrate, nitrogen can be reduced into nitrogen gases in oxygen-poor environments.

Stage	Transformation	Consequence for water
Ammonification	Organic nitrogen → ammonium	Possible increase after organic pollution.
Nitrification	Ammonium → nitrite → nitrate	Oxygen consumption, pH drop, and nitrite formation.
Assimilation	Ammonium → biomass	Temporary biological reduction of dissolved nitrogen.
Soil fixation	Adsorption on clays and organic matter	Mobility often lower than that of nitrates.

What are the sources of ammonium in water?

Natural decomposition of organic matter

Plant residues, dead organisms, and soil organic matter release ammonium during decomposition. In oxygen-poor waters, it can accumulate because nitrification is slowed.

Domestic wastewater

Urine, feces, and wastewater contain ammoniacal nitrogen. A sewer leak, a failing septic tank, or insufficiently treated discharge can contaminate an aquifer or a watercourse.

Livestock and agricultural runoff

Slurry, manure, and animal waste release ammonia and ammonium. Improper storage and uncontrolled spreading can lead to transfer into the water supply.

Nitrogen fertilizers

Certain fertilizers provide ammonium directly or compounds that transform into it, such as urea. Ammonium can be temporarily retained by soils before being nitrified.

Geological origin

Certain deep groundwater sources, which are oxygen-poor and rich in natural organic matter, may contain ammonium without recent pollution.

Industry

Chemical, food processing, oil, paper, textile, cooling, or fertilizer manufacturing industries can produce nitrogenous effluents.

Why can ammonium persist in groundwater?

In an oxygen-poor aquifer, nitrifying bacteria function less efficiently. Ammonium can therefore persist for long periods.

Its positive charge also allows it to be adsorbed onto clays and organic matter, unlike nitrate, which migrates more easily. However, interactions with minerals can gradually release fixed ammonium.

deep and ancient waters;
reducing environments poor in oxygen;
sediments rich in organic matter;
marshy or peaty zones;
confined aquifers;
water intakes influenced by wastewater or agricultural runoff.

Why is ammonium an important indicator?

A high concentration can signal pollution by organic matter or wastewater, especially when accompanied by indicator bacteria, nitrites, or high oxygen demand.

However, ammonium is not always proof of recent pollution. In some deep aquifers, it may be of natural origin. Interpretation must therefore take into account the hydrogeological context and other parameters.

Observed association	Possible interpretation
Ammonium + fecal bacteria	Contamination by wastewater or animal waste.
Ammonium + iron + manganese	Possible natural reducing groundwater.
Ammonium + nitrites	Ongoing or incomplete nitrification.
High ammonium without dissolved oxygen	Reducing environment favorable to its persistence.
Ammonium in a chloraminated network	Excess free ammonia or degradation of chloramines.

What are the effects of ammonium on human health?

The body naturally produces ammonia during protein metabolism and mainly converts it into urea. At concentrations usually found in drinking water, exposure through ingestion is low compared to internal production.

The World Health Organization does not set a specific health guideline value for ammonia in drinking water, as no health effects are expected at normally observed concentrations.

Health Canada also concludes that no health-based value can be established from available data. Concerns primarily relate to indirect effects on water quality and network operation.

Concentrated exposures

Concentrated ammonia is an irritant and corrosive to the eyes, skin, respiratory tract, and digestive tract. These situations do not correspond to ordinary drinking water concentrations.

Hepatic function

In people with severe liver disease, the body's management of ammonia can be impaired. An individual medical situation should be discussed with a healthcare professional without automatically extrapolating from a water analysis.

What are the main indirect effects in drinking water?

Nitrification

Ammonium can be converted into nitrites and then nitrates in filters, reservoirs, and pipes. Nitrite formation is the primary indirect health concern.

Disinfectant consumption

Ammonia reacts with chlorine and can reduce the amount of free disinfectant available. It can also be used intentionally to form chloramines.

Biological development

Ammonium can serve as a nutrient for nitrifying bacteria and contribute to the biological instability of the network.

Taste and odor

At high concentrations, ammonia can contribute to organoleptic issues. Chloramines and reaction products can also change the taste of the water.

Corrosion

Nitrification consumes alkalinity and can lower the pH. These changes can aggravate certain corrosion phenomena and material leaching.

What is the link between ammonium and chloramination?

Chloramination involves reacting chlorine with ammonia to primarily produce monochloramine, a disinfectant that is more stable than free chlorine in certain distribution systems.

The chlorine-to-nitrogen ratio, pH, contact time, and temperature determine the species formed. Improper dosing can produce dichloramines or trichloramines, which are often associated with unpleasant tastes and odors.

An excess of free ammonia also provides a substrate for nitrifying bacteria. Health Canada recommends limiting free ammonia entering the distribution system to less than 0.1 mg/L expressed as nitrogen, and preferably to less than 0.05 mg/L, in order to reduce the risk of nitrification.

What are the reference values for ammonium?

Organization or regulation	Value	Nature of the value
World Health Organization	No health-based guideline value	No health effects expected at concentrations typical of drinking water.
European Union – Directive (EU) 2020/2184	0.50 mg/L	Indicator parametric value for ammonium.
France	0.50 mg/L	Quality reference for water intended for human consumption.
Canada	No health-based value	Recommended management to limit nitrification.
United States – EPA	No specific federal limit	No national regulatory maximum for ammonia in drinking water.
Australia	0.5 mg/L	Aesthetic value related notably to copper corrosion.

In the European Union and France, the value of 0.50 mg/L is an indicator parameter. An exceedance must lead to an investigation of its origin and its consequences on the treatment and the distribution system.

How to convert between ammonium and ammoniacal nitrogen?

The molar mass of NH₄⁺ is approximately 18 g/mol, of which 14 g/mol corresponds to nitrogen.

Conversion	Approximate factor	Example
NH₄⁺ to NH₄-N	Multiply by 14/18, i.e., 0.778	0.50 mg/L NH₄⁺ ≈ 0.39 mg/L N.
NH₄-N to NH₄⁺	Multiply by 18/14, i.e., 1.286	0.10 mg/L N ≈ 0.129 mg/L NH₄⁺.
NH₃-N to NH₃	Multiply by 17/14, i.e., 1.214	0.10 mg/L N ≈ 0.121 mg/L NH₃.

Before comparing a result to a regulatory value, it must be verified whether the report expresses ammonium, ammonia, or ammoniacal nitrogen.

How to analyze ammonium in water?

Colorimetric method

Indophenol blue or salicylate methods produce a coloration measured by spectrophotometry. They are commonly used for drinking and natural waters.

Selective electrode

An ammonia-sensitive electrode can be used after pH adjustment to convert ammonium into ammonia gas. It is suitable for certain concentration ranges.

Ion chromatography

Cation chromatography can separate and quantify ammonium with other cations.

Online analysis

Treatment plants and chloraminated distribution systems can use continuous analyzers for free ammonia, total ammonia, monochloramine, and residual chlorine.

Sampling and preservation

use the bottle and preservative indicated by the laboratory;
avoid contamination from cleaning products containing ammonia;
keep the sample cold if required;
adhere quickly to the analysis deadline;
report the presence of chlorine or chloramine.

How to interpret an ammonium result?

Situation	Possible interpretation	Additional controls
Low, stable concentration	Typical situation in many waters	Standard monitoring.
Sudden increase in a well	Possible recent organic pollution or infiltration	Microbiology, nitrates, nitrites, and well inspection.
Presence in reducing deep water	Possible natural origin	Iron, manganese, dissolved oxygen, sulfides, and geochemistry.
Ammonium accompanied by nitrites	Nitrification in progress	pH, alkalinity, nitrate, disinfectant, and biofilm.
Above 0.50 mg/L in the EU	Exceedance of indicator parameter	Root cause investigation and treatment evaluation.

Which technologies reduce ammonium?

Biological nitrification

Biological filters oxidize ammonium into nitrites then nitrates. The process requires oxygen, a suitable temperature, sufficient alkalinity, and stable biomass.

Zeolites and ion exchange

Certain natural zeolites, notably clinoptilolite, can exchange their cations for ammonium. Capacity depends on water composition and competing ions.

Breakpoint chlorination

A controlled dose of chlorine can oxidize ammonia after reaching the breakpoint. This method requires professional management to avoid by-products and an unsuitable residual.

Ammonia stripping

At high pH, a greater portion of ammonium becomes volatile ammonia, which can be removed by aeration. This process is mainly used for wastewater or industrial water and requires emission management.

Reverse osmosis

Reverse osmosis can reduce ionized ammonium, but performance varies with pH, the membrane, and operating conditions. Non-ionized ammonia may be rejected less effectively by certain membranes.

Electrodialysis

Ion-exchange membranes can separate ammonium and other dissolved ions. This technology is mainly used at a collective or industrial scale.

Distillation

The volatility of ammonia can complicate distillation. A poorly designed device can transfer a portion of the ammonia to the distillate. Performance must be demonstrated.

Standard activated carbon

Conventional activated carbon is generally not considered a reliable technology for removing dissolved ammonium.

Mechanical or ceramic filtration

Ammonium is a dissolved ion and passes through sediment filters as well as ordinary microporous barriers.

Boiling

Domestic boiling is not a reliable treatment method. The amount removed depends on pH, duration, and chemical form, while evaporation concentrates other salts.

Comparison of treatment technologies

Technology	Potential	Points to watch
Biological nitrification	High with controlled operation	Produces nitrates and may temporarily produce nitrites.
Zeolite / ion exchange	Variable to high	Saturation, competing ions, and regeneration.
Breakpoint chlorination	High	Dosing, by-products, and residual chlorine control.
Stripping	High at suitable pH	pH adjustment and emission management.
Reverse osmosis	Variable	Depends on NH₄⁺/NH₃ form and membrane.
Electrodialysis	High	Cost and concentrate management.
Standard activated carbon	Low or not demonstrated	Do not extrapolate from chlorine or organic compounds.
Mechanical filtration	Ineffective	Ammonium is dissolved.

How to evaluate a filter against ammonium?

Reduction must be demonstrated by a specific test. A filter capable of reducing certain metals or chlorine is not automatically effective against ammonium.

Item to verify	Why is it important?
Analyzed form	Distinguish between ammonium, ammonia, and ammoniacal nitrogen.
pH and temperature	Determine the NH₃/NH₄⁺ proportion.
Inlet concentration	Allows evaluation of the test difficulty.
Outlet concentration	Must be interpreted with the exact unit.
Total treated volume	Essential to judge the media capacity.
Competing ions	Strongly influence zeolites and resins.
Nitrite formation	Biological treatment must be monitored along the entire chain.
End-of-life test	Initial performance is not enough.

The performance of a filtration system must be evaluated based on specific tests conducted by its manufacturer. In the absence of published results regarding this contaminant, no numerical reduction can be claimed.

Consult Monderma certifications and analyses

How to prevent ammonium problems in distribution systems?

limit free ammonia after drinking water production;
precisely control the chlorine-to-ammonia ratio in chloramination;
maintain an adequate disinfectant residual;
reduce excessive residence times;
monitor warm zones and network extremities;
control ammonium, nitrites, nitrates, pH, and alkalinity;
clean reservoirs and control biofilms;
implement a reaction plan for nitrification episodes.

What to do in case of ammonium in a private well?

A high result must be confirmed and interpreted with other analyses. It is necessary to verify, notably, nitrites, nitrates, coliform bacteria, Escherichia coli, iron, manganese, pH, conductivity, and dissolved oxygen.

inspect well tightness;
check the distance from septic tanks and effluent storage;
investigate surface water infiltration;
have water analyzed after heavy rain or flooding;
do not conclude it is purely natural in origin without studying the context;
have the treatment sized based on a complete analysis.

Frequently asked questions about ammonium in water

What is the value for ammonium in France?

The quality reference is 0.50 mg/L.

Does the WHO set a health limit?

No. The WHO considers that a specific health-based guideline value is not necessary at concentrations typical of drinking water.

Is ammonium toxic?

At ordinary drinking water concentrations, the main concern is indirect: nitrification, disinfectant consumption, and nitrite formation.

What is the difference between ammonia and ammonium?

Ammonia NH3 is non-ionized, while ammonium NH4+ carries a positive charge. Their proportion depends on pH and temperature.

Why is pH important?

A high pH increases the proportion of non-ionized ammonia, which is more volatile and more toxic to aquatic organisms.

Does ammonium always indicate fecal contamination?

No. It can also be of geological origin in certain reducing groundwater.

Which parameters should be analyzed alongside ammonium?

Nitrites, nitrates, microbiology, iron, manganese, pH, dissolved oxygen, and conductivity.

Why does ammonium cause nitrification?

It serves as a substrate for bacteria that oxidize it into nitrites and then nitrates.

Is nitrification dangerous?

It can produce nitrites, consume disinfectant, lower the pH, and promote biological instability in the distribution system.

Does activated carbon remove ammonium?

Standard activated carbon is generally not a reliable solution for this dissolved ion.

Does a ceramic filter remove ammonium?

No. A simple microporous barrier does not retain dissolved ammonium.

Can zeolite retain ammonium?

Yes, certain zeolites can exchange it, but their capacity depends on competing ions and saturation.

Is reverse osmosis effective?

It can reduce ionized ammonium, but performance depends on the pH, the membrane, and the proportion of non-ionized ammonia.

Does boiling water remove ammonium?

This is not a reliable household method, as the result depends on pH, duration, and chemical equilibrium.

Why does ammonium consume chlorine?

It reacts with chlorine to form chloramines and other reaction products.

What is chloramination?

It is the controlled use of chlorine and ammonia to primarily produce monochloramine as a disinfectant.

What does 0.1 mg/L expressed as nitrogen mean?

This corresponds to approximately 0.129 mg/L of ammonium (NH4+).

Can deep water naturally contain ammonium?

Yes, especially in oxygen-poor environments rich in natural organic matter.

What should be done in case of an exceedance?

Confirm the result, investigate the cause, analyze nitrites and microbiology, and then adapt the treatment.

Can taste or odor be relied upon?

No. An abnormal concentration can be present without any obvious sensory signs.

Scientific and administrative sources

World Health Organization – Ammonia chemical fact sheet
Consult the WHO chemical fact sheet
World Health Organization – Guidelines for drinking-water quality, 2026
Consult the WHO recommendations
European Union – Directive (EU) 2020/2184
Consult the directive on EUR-Lex
Health Canada – Ammonia technical document
Consult the Health Canada technical document
Environmental Protection Agency – Drinking Water Regulations and Contaminants
Consult the EPA information
Monderma – Certifications and laboratory analyses
Consult Monderma certifications and analyses

Contaminants and associated parameters

Nitrites Nitrates Iron Manganese Chlorides Sulfates Sodium Copper

Health warning: this fact sheet is provided for informational purposes. It does not replace an analysis performed by a laboratory, the recommendations of the competent health authority, or the advice of a healthcare professional. An exceedance must be interpreted in conjunction with nitrites, nitrates, microbiological parameters, and the characteristics of the source or distribution system.