The average size of the openings between pieces of the filter media are represented in microns. For example, a 20-micron filter has larger openings than a 5-micron filter. Consequently, the 20-micron filter element will let larger particles pass through the filter than the 5-micron media would. Bacteria range in size from 0.2 to 2 microns in width or diameter and from 1 to 10 microns in length for the nonspherical specie, so a 1-micron filter will remove most bacteria and cysts. If you are on municipal water, the water has already been treated with chlorine, chloramines and/or fluoride to remove bacteria, so chances are you do not have a bacteria problem, unless there is a problem with the water pipes between the water reclamation plant and your home. Although many customer purchase the 1-micron absolute for the kitchen because it can remove some pharmaceutical drugs, too,