There are a couple of things to bear in mind when shopping for filters. First, only a system which includes a n iodine matrix will kill viruses (see below). Second, a filter with pores larger than 0.2 microns - note the location of the decimal point, as it is important - will let bacteria through. The advantages of a filter are quick processing time (don't have to wait for the pot to boil or the iodine to do its work) and clean-tasting water (no iodine or vitamin C flavor). Some systems also contain a carbon filter which will remove chemical toxins.