A disc filter includes a filtrate holding tank disposed below a series of disc-shaped filter members supported on a drum. Filtrate from the holding tank is used to backwash filter media on the disc-shaped filter members. Filtrate is discharged from the holding tank via a filtrate conduit. Bypass water is directed through a bypass conduit in the disc filter and mixed with the filtrate downstream of the filtrate holding tank. This assures that the filtrate used to backwash the filter media does not include bypass water.