The Ceramic Prefilter Disc provides a pore-size of 0.2 microns (0.00022 mm). Bacteria range in size from 0.2 to 5 microns and so bacteria and protozoa (1-15 microns) are efficiently filtered out. The impregnated silver delays the growth of bacteria. Silver ions are attracted to bacteria by polar adsorption. After penetrating the cell membrane, the ions damage the bacteria's DNA, thus preventing further multiplication. The bacteria's respiratory system is attacked and blocked, causing a chain reaction, and as a result the bacteria die.