A standard method used for the indirect measurement of the amount of pollution that is not able to be oxidized biologically in a sample of water. The test procedure is based on the chemical decomposition of organic and inorganic contaminants dissolved or suspended in water. The test indicates the amount of water-dissolved oxygen consumed by the contaminants; the higher the chemical oxygen demand, the higher the amount of pollution in the sample. The quantity of oxidant consumed is expressed in terms of its oxygen equivalence and is expressed in mg L^-1 of oxygen.