A system for calculating a concentration of a water treatment chemical includes a water analyzer, databases storing information regarding a chemical component of the water treatment chemical, a server sending the information stored in the database, and a communication device sending the information acquired from the server to the water analyzer. The water analyzer includes a storage unit storing a calibration curve defining the relationship between the concentration of a chemical component and absorbance, a communication unit receiving the information regarding the chemical component of the water treatment chemical, an irradiation unit irradiating water to be analyzed with light, a detection unit detecting transmitted light, and an arithmetic and control unit calculating absorbance from the result of the detection by the detection unit, acquiring a calibration curve from the storage unit, and calculating the concentration of the chemical component with reference to the acquired calibration curve and the measured absorbance.