A filter assembly for a seawall filters the flow of groundwater through a hole in the wall. The filter assembly includes: (a) a housing containing a flat flange and a perforated conical shell, the shell adapted to extend into the hole with its apex extending toward the landward side, the flange having a seaward side adapted to fit flushly against the seawall, the flange having a landward side connected to the shell, the flange having an opening that defines an open base for the shell; (b) a perforated conical cage having an open base that fits within the shell of the housing; (c) a conical filter element having an open base that fits within the cage; (d) a perforated conical sleeve having an open base that fits within the filter element; and (e) a perforated cap that is removably and flushly fastened to the opening in the flange to secure the cage, filter element, and sleeve within the shell of the housing.