A "polishing" water filter for the micro-filtration of fine particles comprises a porous ceramic substrate, having an average pore size in the range of about 0.2 to about 200 microns, which is coated and impregnated with porous rice hull ash (RHA) particles that have an average particle size that is greater than the average pore size of the ceramic substrate. The ceramic substrate preferably has an average pore size of about 30 microns; the RHA has an average particle size in the range of about 120 to about 150 microns and an average pore size in the range of about 0.5 to about 10 microns.