If you are looking at water filters that will clean your water to prevent illness, here are the NSF (National Sanitation Foundation) industry standards that a "wilderness" filter should meet:
Protozoan Cysts: ≥99.9% removal
Bacteria: ≥99.9999% removal
Virus: ≥99.99% removal
Please note that I am not a water expert, but I am summarizing from many articles I consider reliable and the above standards are accepted nationally. You should be aware that the symbols in the list above mean "greater or equal to" --- and if a filter manufacturer waffles on their numbers, beware! Phrases like "up to" a certain level are not the same as "equal to or greater than."
You must also pay attention to how many "nines" are shown for each type of contaminant as they are necessary for the size of the particles being filtered out.
When the characters in the third and final novel in the Obliterated series settle in a permanent location, establishing a year-round water supply is the first priority on their list. They use a variety of ways to filter and purify their water. See the book on Amazon.