Nitrate (NO3-) is a water-soluble compound that occurs naturally but becomes a contaminant when its levels are elevated in drinking water sources. Sources of contamination include agricultural runoff from nitrogen-based fertilizers, animal waste from feedlots, and faulty septic systems. Elevated nitrate levels pose a significant public health risk, particularly to the most vulnerable members of the population. The most severe health concern is methemoglobinemia, commonly known as “blue baby syndrome,” where nitrate is converted into nitrite, which reduces the blood’s ability to carry oxygen, especially in infants under six months of age. Understanding the level of contamination and the appropriate treatment method is the first step toward safeguarding a household’s water supply.
Identifying Nitrate Contamination Levels
Nitrates are odorless, colorless, and tasteless, meaning the only way to determine their presence is through laboratory testing. The US Environmental Protection Agency (EPA) has established a Maximum Contaminant Level (MCL) for nitrate in drinking water at 10 milligrams per liter (mg/L), measured as nitrate-nitrogen (NO3-N). If testing indicates levels exceeding this concentration, immediate action is necessary to treat the water or find an alternative source.
While home testing kits can offer a generalized idea of contamination, a certified laboratory test provides the necessary accuracy to guide treatment decisions. For private well owners, annual testing for nitrates is a standard recommendation, especially if the well is shallow or located near agricultural activity. Boiling water does not remove nitrates; instead, the process concentrates the contaminant as the water evaporates.
Point-of-Use Removal Systems
For treating small volumes of water intended only for drinking and cooking, Point-of-Use (POU) systems offer effective solutions that rely on physical separation.
Reverse Osmosis (RO)
Reverse Osmosis is one of the most common POU methods for nitrate removal, often installed under a kitchen sink to treat water at a single tap. The RO system forces water under pressure through a semi-permeable membrane that physically blocks molecules larger than water, including the nitrate ion. The treated water is then stored in a small tank, while the rejected contaminants are flushed down the drain in a brine solution. While RO systems are generally faster and more cost-effective to run than other POU options, the system does produce wastewater as part of the purification process.
Distillation
Distillation is another highly effective POU method that achieves nitrate removal rates of approximately 98%. This process involves heating the contaminated water to create steam, which leaves the dissolved solids, including nitrates, behind. The steam is then cooled and condensed back into liquid water. Distillation units are slower and typically require more energy to operate than RO systems, though they are suitable for those seeking a high-purity water source at a specific location.
Whole-House Ion Exchange Solutions
For households requiring treatment of all incoming water, ion exchange is often the most practical and efficient method for high-volume nitrate removal. This process uses a tank filled with specialized resin beads that facilitate a chemical exchange. The system is an Anion Exchange, where the negatively charged nitrate ions in the water are selectively exchanged for chloride ions held by the resin.
The resin beads eventually become saturated with nitrate and must be regenerated to restore their removal capacity. Regeneration is achieved by flushing the resin with a concentrated salt brine solution, which releases the trapped nitrates and replaces them with fresh chloride ions. This process uses a different type of resin designed specifically to target anions like nitrate.
A consideration with anion exchange is that other negatively charged ions, such as sulfate, can interfere with the nitrate removal efficiency, as the resin may preferentially adsorb sulfate. The regeneration process produces a saline waste brine that must be properly disposed of, and the treated water will have an increased chloride concentration.
Preventing Future Contamination
Preventative measures at the source reduce the burden on treatment equipment. For private well owners, ensuring the well is properly maintained and sealed prevents surface water runoff from entering the water supply. This includes securely capping the well and routinely inspecting the casing for any cracks or damage.
Proper management of waste and chemical sources near the well is also effective in preventing contamination. Septic systems should be regularly inspected and pumped, typically every three to four years, to prevent seepage of nitrogenous waste into the groundwater. Additionally, the use of fertilizers and manure should be carefully managed, ensuring they are not stored or applied near the well or in areas where runoff can easily reach the water source.