Cyanide is a pollutant that originates mostly from metallurgic, galvanic and other industrial processes, such as gold and silver extraction. Because it is poisonous to the human nervous system, it is imperative to monitor and control cyanide levels in portable water. When in contact with acids, cyanide is freed as a poisonous gas.

The Environmental Protection Agency (EPA) has established that the maximum level of cyanide in water is not to exceed 0.2 mg/L (ppm).