A water treatment system of the present invention for effluent generated in a plant facility includes: a flue gas treatment system 18 that performs treatment of boiler flue gas 12 from a boiler 11; and a spray drying device 23 that includes a spraying unit, which sprays effluent 22 generated, for example, in a cooler 21 of the plant facility, and that performs spray drying using part 12a of the boiler flue gas 12. The water treatment system draws the effluent 22 is discharged into the spray drying device 23 so as to dry the sprayed liquid by the part 12a of the flue gas 12. It is thus not necessary to separately perform treatment of the effluent 22 in an industrial effluent treatment facility and it is possible to eliminate the need of draining the effluent 22 generated in the plant.
