Filters will remove bacteria and protozoans. Protozoans are big, 1-15 microns but bacteria could be much smaller. To be safe I would personally use a filter having a pore length and width of.2 microns. You may get by having a pore dimensions of .3 or .4.but why take chance. With filters completely have to clean them out and replace the replacements.The hikers were hoaxers and the huffy crypto-zoological...