How it works: Filtering water, which physically strains it, skims off larger organisms like protozoa and bacteria, and removes chunks, but isn’t effective against viruses. So use it at home but not abroad, unless it is also a purfier. For international travel, always use a purifier effective against viruses, bacteria and protozoa.
Pros: Filters don’t run out, like chemical treatments. Some—gravity filters—don’t even require pumping, and they can handle a much larger volume of water easily. Some filters not only strain pathogens and organic matter, but also purify it. Those with carbon in the filter also make your water taste better.
Cons: Filters are bulkier and heavier than a small bottle of chemical treatment—though some waterbottle straw models are relatively compact and convenient. Unless a filter is also a purifier, it’s not the best choice for international travel—most can’t catch viruses. Filters can clog, so they may need field flushing and occasional chemical cleaning.
What you need: MSR Sweetwater Purification System or the chemical-free First Need XLE Portable Water Purifier are do-it-all purifying filters. Non-purifying filters include the MSR Miniworks EX and Katadyn Vario.