In this study, a porous Al alloy filter was designed for water purification systems. The combination of higher permeability for fluid flow and excellent filtering characteristics for removing pollutants is required for water purification. The filter's macropore structure was controlled by a powder metallurgical process using granulated powders for high permeability and its micropore structure was generated by alkali surface modification on the macroporous sintered body for enhanced filtration efficiency. After surface modification, the specific surface area was increased by 10 times over the as-sintered specimen. Phosphate filtering characteristic was noticeably improved by a ligand exchange between phosphate and aluminum hydroxide formed by alkali surface modification.