This Standard specifies the method for determination of orthophosphate contained in industrial Water, industrial wastewater, etc. by using the flow analysis by molybdenum blue absorption spectrophotometry and the method for determination of total phosphorus by the flow analysis including the pretreatment in which phosphorus compounds in the sample are oxidized to orthophosphate by the heat oxidation-decomposition using peroxodisulfate. The method is also applicable to surface water, ground water, seepage water, etc.