A water-resistant cover assembly for an electrical outlet box includes a gasket sized to substantially cover the open side of the electrical outlet box, an adapter plate and a cover adapted to engage the mounting screw of the electrical fixture for mounting the cover to the outlet box. The adapter plate has an opening sized and shaped to receive a portion of the electrical fixture therein, and further includes a projection extending from a back face thereof. The projection pierces through the gasket to be frictionally held thereto and has a size adapted to be received in the aperture of the electrical fixture for aligning the adapter plate and the gasket thereto. The cover has an opening for providing access to the electrical fixture and is adapted to sandwich the adapter plate and the gasket against the electrical fixture when mounted to the outlet box.