Nitrogen in drinking water is a common concern in water quality reports. While nitrogen gas is harmless and makes up nearly 78% of the atmosphere, certain water-soluble chemical forms pose a health risk. The safety concern focuses on two related inorganic compounds, nitrate and nitrite, which are products of the natural nitrogen cycle that can accumulate due to human activity. These compounds are colorless, odorless, and tasteless, meaning their concentration must be determined through laboratory testing. Understanding the difference between these two compounds and how they interact with the body is essential for assessing water safety.
Understanding Nitrate and Nitrite Contamination
Nitrate and nitrite are two distinct nitrogen ions that are naturally occurring but become contaminants at elevated levels. Nitrate is the more stable and common form found in water supplies, consisting of one nitrogen atom bonded to three oxygen atoms. Nitrite is less stable, composed of one nitrogen atom and two oxygen atoms, and is typically found in much lower concentrations in groundwater. Nitrate can be reduced to nitrite under certain conditions.
This reduction often occurs in low-oxygen environments, such as saturated soil or within plumbing systems. More significantly, nitrate is converted to nitrite inside the human body by bacteria in the digestive tract. This conversion is what makes nitrate a concern, as the resulting nitrite ion causes the immediate and acute health effects. The presence of nitrite in the water usually indicates a recent source of contamination, since it quickly converts to the more persistent nitrate form in oxygenated water.
Health Impacts of Ingesting Nitrogen Compounds
The most severe health risk associated with consuming water contaminated with high levels of nitrate and nitrite is methemoglobinemia, commonly known as Blue Baby Syndrome. This acute illness primarily affects infants under six months of age. The danger arises when ingested nitrate is converted to nitrite, which enters the bloodstream and interferes with the body’s ability to transport oxygen.
Nitrite reacts with the iron in hemoglobin, the protein in red blood cells responsible for carrying oxygen. This reaction changes the hemoglobin into methemoglobin, which cannot bind oxygen effectively. This leads to a reduction in the blood’s oxygen-carrying capacity. Symptoms of oxygen deprivation include a bluish-gray discoloration of the skin, known as cyanosis.
Infants are uniquely vulnerable because several biological factors are not fully developed until they are around four to six months old. They have a higher gastric pH, which allows bacteria that facilitate the nitrate-to-nitrite conversion to thrive. Infants also consume a higher volume of water relative to their body weight, increasing their exposure dose. Furthermore, they possess lower levels of the enzyme responsible for converting methemoglobin back into functional hemoglobin.
Long-term exposure to elevated nitrate levels presents other concerns for the general population. In the adult stomach, nitrite can react with compounds found in proteins to form N-nitroso compounds (NOCs). These NOCs are known to be carcinogenic and have been linked in some studies to an increased risk of cancers, particularly of the stomach, colon, and bladder. This chronic risk remains an area of ongoing scientific investigation.
Sources of Water Contamination and Safety Standards
The presence of nitrate and nitrite in drinking water results mainly from agricultural practices and the management of human and animal waste. Agricultural runoff is a major source, as excess application of nitrogen-based fertilizers and animal manure can leach into the groundwater after rain or irrigation. Since nitrate is highly soluble, it moves easily through the soil and into aquifers that supply wells and public water systems.
Septic systems and wastewater treatment discharges also contribute to contamination, especially in rural areas. Nitrogenous waste products are oxidized in the soil, forming nitrate that can eventually reach the water supply. Shallow wells and wells located in sandy soils are particularly susceptible because there is less natural filtration before the water reaches the well.
To protect public health, regulatory bodies like the U.S. Environmental Protection Agency (EPA) have established enforceable limits. The Maximum Contaminant Level (MCL) for nitrate is set at 10 milligrams per liter (mg/L), measured as nitrate-nitrogen. For nitrite, the MCL is significantly lower, at 1 mg/L (as nitrite-nitrogen), reflecting its higher immediate toxicity. These federal standards are mandatory for all public water systems.
Testing Your Water and Effective Treatment Options
Testing is the only reliable way to determine if nitrogen compounds are present in a drinking water source because they have no noticeable taste, color, or odor. Private well owners are not subject to the mandatory testing and monitoring required of public water systems. It is recommended that private wells be tested for nitrate and nitrite at least once a year, and immediately after any well construction, repair, or change in water quality.
Water samples must be analyzed by a state-certified laboratory, which provides instructions for proper collection. If testing reveals a nitrate level above 10 mg/L, or approaching 5 mg/L when infants are present, immediate action is necessary. This includes securing an alternative water source, such as bottled water, especially for preparing infant formula. Identifying and correcting the source of contamination, such as a failing septic system, is also a necessary first step.
For long-term remediation, several treatment methods are effective at removing nitrate and nitrite from drinking water. Boiling water is not effective, as the water evaporates and concentrates the nitrate, making the resulting water more hazardous. Effective methods include reverse osmosis (RO) systems, which force water through a semi-permeable membrane to filter out contaminants. Ion exchange units function similarly to water softeners, using a resin to swap nitrate ions with a non-toxic ion like chloride. Distillation is another viable method that boils the water into steam and then then condenses it back into liquid, leaving the inorganic contaminants behind.