Nitrates are present in nature as a result of decomposition of organic microorganisms or due to their use as fertilizers. Nitrates reduce to nitrites, which in turn easily combine to form substances dangerous to man. A maximum level of 45 mg/L (ppm) is established as a worldwide guideline for nitrate concentration in water. In Europe, the maximum consented level of nitrates in potable water is 50.0 mg/L (ppm), while in the USA the EPA has established a guideline for the maximum level of nitrate nitrogen of 10 mg/L (NO-3-N), which corresponds to 45.0 mg/L of nitrates.