Water quality management system and method for operating water quality management system

A water quality management system 10 provided with: a regenerating ion exchange device 1; a water quality-measuring device 2 with an ion concentration meter 22; a first discharge pipe 3 through which treated water W1 discharged from the regenerating ion exchange device 1 flows; and a second discharge pipe 4 that branches from the first discharge pipe 3 via an automatic valve 5 and is for supplying treated water W1 to the water quality-measuring device 2. With said water quality management system, it is possible to stably reduce the concentrations of sodium ions (Na+) and chloride ions (Cl-) in the treated water discharged from the regenerating ion exchange device used in a primary pure water system of an ultrapure water-producing apparatus and it is possible to thereby limit short term fluctuations in sodium ion (Na+) concentration and chloride ion (Cl-) concentration in the treated water discharged from a non-regenerating ion exchange device used in a subsequent subsystem.