Nitrogen (N) and water
“Nitrogen in water” describes several distinct substances, not just elemental nitrogen gas. Molecular nitrogen (N₂) is abundant in air and dissolves physically in water; reactive forms such as nitrate, nitrite, ammonium and organic nitrogen are the forms most relevant to water quality, treatment and aquatic ecosystems.
Nitrogen forms and the nitrogen cycle
Microorganisms transform nitrogen between ammonium, nitrite and nitrate through processes including nitrification and denitrification. The form found in a sample depends on oxygen, biological activity, pH and other conditions. Nitrogen gas can also be dissolved in water and is measured in groundwater studies as a tracer of recharge and microbial processes.[1]
Sources and effects of nitrogen in water
Nitrate and ammonium can enter water from fertilizer and manure, wastewater, septic systems, and natural decomposition. Excess nitrogen discharged to lakes, rivers and coastal waters can promote algal and plant growth, contributing to eutrophication and low dissolved oxygen. The scale of the effect depends on the receiving water and on phosphorus and other limiting nutrients.
High nitrate or nitrite in drinking water can affect oxygen transport in the blood, with bottle-fed infants being a particularly sensitive group. WHO guideline values are 50 mg/L for nitrate as NO₃⁻ and 3 mg/L for nitrite as NO₂⁻; where both occur, the sum of each concentration divided by its respective guideline value should not exceed 1. Local legal standards may differ, and results must be compared using the same reporting basis (as ion or as nitrogen).[2]
Nitrogen removal and treatment
Source protection is the preferred way to prevent nitrate contamination. For drinking-water treatment, nitrate can be reduced by anion ion exchange, reverse osmosis or electrodialysis; these processes transfer nitrate into a residual stream that needs appropriate management. Biological denitrification is widely used for water and wastewater applications when designed and operated for the specific flow and water chemistry. Nitrite can be oxidized to nitrate by disinfection, but this does not remove total nitrogen. Treatment selection should be based on analysis of the nitrogen species and the required finished-water quality.[3]
For an overview of common ammonia, ammonium, nitrate and nitrite compounds, where they occur, and treatment options, see common nitrogen-containing salts in aqueous solutions and their removal/purification technologies.
Last reviewed: 3 November 2026 by Lenntech.
Sources and further reading
- U.S. Geological Survey: Dissolved nitrogen and other gases in groundwater.
- WHO: Chemical fact sheet — Nitrate and nitrite.
- U.S. EPA: National Primary Drinking Water Regulations.
- U.S. EPA: Nutrient pollution.
Literature and the other elements and their interaction with water