GB/T 11914-1989 is a water quality testing standard. Chemical oxygen demand (COD) is determined by dichromate method. COD reflects the degree of pollution of reducing substances in water and is a key indicator for evaluating water quality. The standard elaborates on the operation process from water sample digestion, potassium dichromate oxidation, to ferrous sulfate ammonium titration and calculation of COD value. The method is classic and reliable. It is suitable for all kinds of water samples. It provides important data support for water quality monitoring, pollution control, environment assessment, etc., and helps to control and improve the water environment mass.