Many of the water filters carried by backpackers and long-distance hikers are unable to remove microorganisms in proportions smaller than 3 microns.
While protozoa such as Giardia (shown below) and Cryptosporidium are in proportions of about 5 microns, water filtration systems are missing bacteria such as cholera, E. coli, and salmonella (0.2-0.5 microns) and
Once you filter your drinking water, the safe solution is to always use a drinking water purifier such as chlorine dioxide. Like filter systems, however, these chemical substances have limitations that you will need to learn to avoid getting tired. Nothing on the trail can come even with reverse osmosis filters in homes, but most hiking filters can come kinda close in taste and safety.
All chemical chemicals have a water purification problem that has sediment because the allergens suspended in this inflatable water impede the chemical reaction. Therefore, filtering to remove the sediment or to make the sit overnight can be done before purification is preferred by the particles.
In addition, if your normal water is below 60 levels F, the purification process will be slowed down in winter. In most thumb cases, the recommended contact time should be twined for each and every 20 F levels below 60 F levels.
P.S. I started kayaking whitewater in October 2007 with a good friend and kayak coach who is in charge of the chemical executive unit responsible for certifying normal water purification solutions for the entire U.S. Military. The military. He was adament that the combination of water purification and purification is necessary for traveling backcountry in the eastern United States, which is why I quote above.