This standard specifies a method for the determination of ammonium content in drinking water, surface water and wastewater using Noll's reagent Colorimetry. This method is suitable for the determination of samples with a maximum sample volume of 50mL and an ammonium nitrogen concentration of up to 2mg/L. Noll's reagent reacts with ammonium in the sample to form a yellow-brown complex. Its concentration is determined by visual Colorimetric or Spectrophotometric method, spectrophotometry. Suspended solids, residual chlorine, metal ions and organic matter may interfere with the determination, and pretreatment is required to eliminate the interference. The minimum detection concentration of this method is 0.02mg/L, which is suitable for environment water quality monitoring and analysis.