Nitrate is a chemical compound composed of nitrogen and oxygen, naturally found in the environment as part of the nitrogen cycle. Tap water commonly contains nitrates, though public supplies usually maintain low concentrations to meet safety standards. Elevated levels in drinking water are predominantly a result of human activities. This contamination becomes a public health concern when concentrations rise above established safety limits.
Where Nitrates Come From
High nitrate levels in water sources are primarily linked to the widespread use of nitrogen-based compounds on land. Agricultural runoff is a major contributor, as synthetic fertilizers like ammonium nitrate and potassium nitrate are highly water-soluble. When more fertilizer is applied than crops can absorb, the excess nitrate leaches through the soil with rainwater or irrigation and enters both surface water and groundwater aquifers.
Animal waste and manure from livestock operations, especially concentrated animal feeding operations (CAFOs), also introduce significant amounts of nitrogen. This organic nitrogen is broken down by microbial action into nitrate. Human waste from septic systems and sewage discharge represents another substantial source of contamination.
Since nitrate does not bind to soil particles, it migrates easily with the flow of water. These sources lead to high nitrate concentrations, particularly in shallow, domestic wells located near agricultural fields or failing septic systems, making groundwater an especially vulnerable reservoir for the contaminant.
Health Risks of Nitrate Exposure
The most serious health threat from consuming nitrate-contaminated water is to infants under six months of age, who risk developing methemoglobinemia, commonly known as “Blue Baby Syndrome.” In the infant’s digestive system, naturally occurring bacteria convert the ingested nitrate into nitrite. This conversion is more pronounced in infants due to their lower stomach acidity.
The nitrite then enters the bloodstream and reacts with hemoglobin, the protein responsible for oxygen transport. It oxidizes the iron in hemoglobin, which creates methemoglobin. Methemoglobin is unable to bind or carry oxygen effectively, leading to oxygen starvation in the body.
Symptoms of methemoglobinemia include shortness of breath and a bluish discoloration of the skin, particularly around the mouth, nose, and nail beds. The condition can progress rapidly and is a medical emergency. Pregnant women are also considered a sensitive population, as some studies suggest a possible link between high nitrate ingestion and risks such as preeclampsia and certain birth defects.
Understanding Legal Limits and Monitoring
The quality of public drinking water is regulated by the Environmental Protection Agency (EPA) under the Safe Drinking Water Act. The EPA sets the Maximum Contaminant Level (MCL) for nitrates in public water systems to prevent methemoglobinemia in infants.
The established MCL for nitrate is \(10\text{ milligrams per liter (mg/L)}\), measured as nitrogen. Public water suppliers are required to regularly test their water for nitrate levels. If testing reveals that the nitrate concentration exceeds the \(10\text{ mg/L}\) MCL, the water system must take corrective action and notify all consumers of the violation.
This federal regulation ensures a baseline of safety for the public water supply. However, these standards and testing requirements do not apply to private wells, meaning homeowners with private water sources are responsible for their own testing and treatment.
Home Treatment Methods for Nitrate Removal
For individuals concerned about nitrate levels in their private well or public supply, three primary technologies are highly effective for home removal. Reverse osmosis (RO) systems force water through a semi-permeable membrane that rejects nitrate ions, typically achieving a reduction efficiency of over 80%. These are most often installed as point-of-use units under the kitchen sink.
Ion exchange is another reliable method, operating similarly to a water softener but using an anion exchange resin to exchange the nitrate ions for harmless chloride ions. Distillation units remove nitrates by boiling the water to create steam, which is then condensed back into purified liquid, leaving the non-volatile nitrate compounds behind in the boiling chamber.
Simple boiling of tap water does not remove nitrates. Because nitrate is a dissolved mineral compound, it is non-volatile and cannot evaporate with the water.
As the water boils away into steam, the remaining liquid volume decreases, which results in a higher, more concentrated level of nitrates. If nitrate levels are confirmed to be high, using tested bottled water is a necessary alternative for preparing infant formula.