What is nitrate? Nitrogen is one of the primary nutrients necessary for plant growth. The most common source of nitrogen used by plants is the nitrate ion, which is a combination of nitrogen and oxygen. Nitrate is created from other nitrogen compounds (i.e. organic matter, nitrite, ammonium, and nitrogen gas) by bacteria in the soil.

Why does nitrate in the groundwater need to be monitored? When present in drinking water in high concentrations, nitrate can present a health risk. As previously-mentioned, the EPA water quality standard (10 mg/l of nitrate-nitrogen or 45 mg/l of nitrate) was set based on the causation of methemoglobinemia in infants and the elderly but studies have also shown a potential link between high nitrate concentrations and cancer, caused by the formation of nitrosamine compounds in the stomach.

Can high nitrate concentrations in water affect livestock? High nitrate-nitrogen concentrations can also cause methemoglobinemia in livestock, although livestock are less susceptible to methemoglobinemia than humans. In general, water with a nitrate-nitrogen concentration in excess of 100 ppm is considered potentially harmful to livestock, although this limit is also dependent on the quantity of nitrate in feed and the age of the animal.

What causes high concentrations of nitrate in water? High nitrate concentrations in the groundwater may occur naturally but usually they are a result of human influence. Nitrate is highly soluble and water entering the soil from precipitation or irrigation will carry nitrate not used by plants down to the groundwater. Nitrate may enter the groundwater from non-point sources (sources that contribute nitrate over a broad area), such as agriculture fertilizers, or from point sources (sources that introduce nitrate at a single location), such as feedlots, septic systems, chemical spills, leaking chemical storage facilities, and improperly abandoned wells. While infiltrating water conveys excess nitrate to the groundwater tending to increase nitrate concentration over time, diffusion and dispersion can decrease nitrate concentration but they do not change the amount of nitrate. Nitrate entering the top of the aquifer will slowly mix with water deeper in the aquifer, tending to decrease nitrate concentration at the top of the aquifer but increasing the concentration at greater depths. Nitrate removed from the aquifer in the pumped water has no effect on nitrate concentration over time. In general, the nitrate concentration in the District is gradually increasing over time (about 0.04 mg/l/year); although, in some locations it is decreasing.

What do I do if my water has a high nitrate concentration? If your water exceeds the acceptable nitrate-nitrogen standard (10 mg/l), health risks can be reduced by using an alternate water supply (i.e. bottled water or water from a well with an acceptable nitrate concentration) or treating the water. Treatment options include distillation, reverse osmosis, or ion exchange, and a description of these techniques is provided below.

Nitrate Treatment Options

Nitrate treatment options include distillation, reverse osmosis or ion exchange. Distillation heats the water to boiling, collects the steam, and condenses it by means of a coil. This process can remove almost 100% of the nitrate. Simply boiling water does not remove nitrate and will increase the nitrate concentration. Reverse osmosis applies pressure to the water and forces it through a semipermeable membrane that filters out the nitrate. Typically, this removes about 85% to 95% of the nitrate. Ion exchange uses special resins that exchange chloride ions for sulfate and nitrate ions as the water passes through the resins, similar to a water softener, and can remove about 90% of the nitrate. Of these methods, reverse osmosis and ion exchange are the most common methods used for residences and will be the only method discussed below. Table 1 provides a comparison between reverse osmosis and ion exchange treatment systems. The nitrate treatment systems also come in Point-of-Entry (POE) and Point-of-Use (POU) systems. POE systems treat water before it enters the home so all of the home’s water will be treated. Their cost ranges between $1,000 and $5,000 as of 2018. POU systems treat water where it is used. For instance, a POU system could be hooked up under the kitchen sink and only treat the water that comes out of that faucet. POU systems cost generally varies between $100 and $1,000.

Table 1: Nitrate Treatment Option Comparison