>>856001This guy got it mostly right. 0.45 will NOT filter all bacteria and some pathogens go through that filter as well as sporulated forms from other pathogens. For that you will need 0.22 uM filter which anyway won´t help with viruses which are smaller. All this only matters if you are extremely concerned for your water safety.
With a 0.45 uM filter you will filter out all protozoa and amoeba which will rule out the always fun giardiasis and you´ll avoid the nasty achantoamoeba. These are much more common pathogens in the wilderness and thus the 0.45 uM filter is useful.
In the end it all depends where are you going, the higher animal activity in the area the higher the risk of pathogens in fresh water, it is specially important to know if there´s cattle roaming around which is the absolute main source (gotta catch that rare anthracis out there for the keks).
You can safely /out/ without filters if you´re high enough and able to drink from the source. Most of the stomach cramps from drinking fresh water come from the fact that we are gigantic faggots used to bottled water and treated tap water so as soon as you drink a bit of different stuff your microbiota goes batshit crazy and starts aborting everything and you feel like shiting your insides out. When you get an actual infection is basically the same but worse
