Nitrates are present in nature as the
result of the decomposition of organic microorganisms or as a
consequence of their use as fertilizers in agricultural industry.
Nitrates reduce to nitrites, which in turn easily combine to form substances
dangerous to man.
A maximum level of 45 mg/L is established as
a worldwide guideline for nitrate concentration in water. In Europe, the
maximum allowed level of nitrates in potable water is 50.0 mg/L, while in
the USA the EPA has established a guideline for the maximum level of nitric
nitrogen of 10 mg/L, which corresponds to 45.0 mg/L of nitrates.