Chemical Oxygen Demand a measurement of the oxygen required to oxidize soluble and particulate organic matter in water. COD is an important water quality parameter because, similar to BOD, it provides an index to assess the effect discharged wastewater will have on the receiving environment. Higher COD levels mean a greater amount of oxidizable organic material in the sample, which will reduce dissolved oxygen levels (DO). A reduction in DO can lead to anaerobic conditions, which is deleterious to higher aquatic life forms.