Abstract: Disclosed is a water filtration medium capable of removing heavy metals from ground water and surface supplies. This medium comprises a gamma form of manganese dioxide that has been comminuted and divided into fractions according to mesh size, including fractions of 10 to 40 mesh, 40 to 100 mesh, and 100 to 325 mesh. The particles in a given mesh size are treated with a reducing agent such as ferrous sulfate and then washed with water to remove iron precipitates and fines. The washed particles are treated with a solution of sodium hydrosulfite and sodium bisulfite. The treated particles are then neutralized with sodium hydroxide to remove remaining acidity. The neutralized particles are washed again in order to remove spent chemicals and undissolved metals. The particles are then dried prior to use as a filtration medium. Also disclosed is a disposable cartridge for housing the filtration medium, a method of using the medium, and a means for preparing the medium.