In the wet addition method, the powdered activated carbon is quantitatively conveyed by a screw precise feeder into the preparation tank. Then, a certain proportion of tap water is added to prepare a suspended slurry with a concentration of 5% to 10%. After that, it is quantitatively added through a dosing pump. The designed dosing amount of powdered activated carbon is generally 10 to 30 mg/L. For some water sources with extremely poor quality, the maximum dosing amount can even reach 50 mg/L.