A monovalent anion. Nitrate salts are highly soluble and do not cause a RO scaling problem. Nitrate, along with ammonia gas and ammonium, is a nitrogen-based ion whose presence is tied with nature’s nitrogen cycle. The primary sources of nitrogen introduction in a feed water come from decomposing animal and plant waste, septic systems, animal feed lot runoff, or agricultural field runoff from fields fertilized with ammonia. In well water sources, ammonia and ammonium are not found, having been converted to the transitory nitrite ion by certain types of bacteria in soils and then oxidized into the more prevalent nitrate ion. Frequently, nitrate concentrations are reported as "ppm as nitrogen" in water analysis and not as "ppm as nitrate" as required for RO projections. To convert "ppm as nitrogen" to "ppm as nitrate", multiply "ppm as nitrogen" by 4.43. The US EPA has set a maximum recommended limit of nitrate at 10 ppm as nitrogen (44.3 ppm as nitrate) for potable drinking water. Nitrates are harmful in that they compete with oxygen for carrying sites in blood hemoglobin. The reduced oxygen content can result in the "blue-baby syndrome" which is why babies and pregnant women are at higher risk to the effects of nitrates.