To provide a method for managing a water treatment system comprehensively, economically and efficiently.

The water treatment system is provided with a plurality of measuring means and an input unit for converting the result of the measurement to digital data. The unit 23 is connected with a CPU 24, which is connected with an output unit 25 and a daily management and abnormality reporting system 26. Furthermore, the system 26 is connected with a central management system 28 through a communication line 29 consisting of an optical fiber, etc. The system 28 compares the quality and intake of raw water A, the quality and quantity of pure water D, a sales amount and sales quantity, and the judgment of deterioration degree concerning each constitutional element with each other to predict the replacing time of constitutional elements and to detect a discrepancy concerning each data.