GB/T 7481-1987 is a water quality testing standard. The ammonium content in water is determined by the Spectrophotometric method, spectrophotometry of salicylic acid. Ammonium is common in natural water bodies and domestic and industrial drainage, and its content affects the ecological equilibrate and water quality safety of water bodies. The standard details the process from water sample collection, pretreatment, to adding salicylic acid and other reagents to develop color, and then measuring Absorbance by spectrophotometer to determine ammonium content. The method has standardized operation and high accuracy. It is suitable for all kinds of water sample testing. It provides key data support for water quality monitoring, water pollution control and related research, and helps maintain a good water environment.