A slider window assembly for a vehicle includes at least one fixed window panel and a movable window panel that is movable along an upper rail and a lower rail at the at least one fixed window panel between an opened position and a closed position. The lower rail includes a U-shaped channel and an attaching structure for attaching the lower rail at the at least one fixed window panel. The lower rail includes a plurality of water drainage channels established at the attaching structure and having an inlet at a wall of the U-shaped channel. A plurality of water diverters are established at the U-shaped channel and are configured to divert water flowing along the U-shaped channel toward the side of the channel along which respective inlets for respective water drainage channels are disposed.