Best water filters for backpacking

Hollow fiber, high flow, very light, and cleanable forever. The reference filter.

This is the filter most American backpackers use and the one to buy unless you have a specific reason not to. A 0.1 micron hollow fiber membrane physically strains out bacteria and protozoa -- which is what North American backcountry water actually contains -- and because you clean it by backflushing rather than replacing a cartridge, there is no consumable cost. It threads onto standard bottles, which means it works as a squeeze filter, inline on a hose, or hung as a gravity system. Two rules: replace the flimsy included pouches with a sturdier bottle, and never let it freeze.

Faster than the Sawyer out of the box, with a reservoir designed to actually work with it.

The practical upgrade over a basic squeeze filter, and the cleaning design is why. Backflushing a Sawyer requires a small syringe that lives in a pocket until you lose it; this one cleans by filling and shaking, which means it gets done at every water source rather than once a season. That matters because flow rate degradation is almost entirely a cleaning problem. Paired with a reservoir it becomes a good group gravity system. It is more sensitive to silty water than the Sawyer, so prefilter through a bandana in muddy conditions.

Drink straight through it at near-bottle speed. Fast, light, and the shortest-lived filter here.

The right filter if you drink as you go rather than filtering into bottles. Flow is fast enough that drinking through it feels close to drinking from a plain bottle, which removes the main friction that stops people filtering often. The collapsible flask packs flat when empty. The honest trade is longevity: the flask seams and cap are the parts owners report failing, and the stated filter life is shorter than the Sawyer's. Buy it for fast-moving days, and carry a backup treatment method on longer trips.

A press-style purifier that removes viruses too. Heavy, slow per liter, and the right tool abroad.

This is a purifier rather than a filter, and that distinction is the reason to buy it. Hollow fiber filters strain out bacteria and protozoa but viruses are too small to be caught, which is fine for North American backcountry water and not fine where the water supply is uncertain. For international travel, this handles tap water in places you would not drink it, murky water, and sources with chemical contamination. The costs are weight, bulk and throughput -- it fills one bottle at a time, so it is a travel tool rather than a group backpacking system.

A self-cleaning pump purifier that handles silt and viruses. Expensive, heavy, and nearly indestructible.

The expedition answer, included because the freezing tolerance is genuinely unique here. Every hollow fiber filter is destroyed by freezing -- the ice cracks the fibers invisibly and the filter is then unsafe without any sign of damage -- and this one is rated to survive it. It also self-cleans on every pump stroke, so flow does not degrade in silty water, and it removes viruses. All of that is bought with weight, bulk and a high price. For ordinary American backpacking it is far more purifier than the water requires.

Chlorine dioxide drops that weigh almost nothing and cannot freeze or clog. Slow, and they do not filter.

Not a filter, and on this page precisely because of that. Chlorine dioxide treats water chemically, which means nothing can clog and nothing can freeze, and it weighs so little that carrying it as a backup to a filter costs you nothing. That combination makes it the best insurance against a filter failing mid-trip. The limitations are waiting time -- substantial, and much longer for protozoa in cold water -- and the fact that it does not remove particulates, so murky water remains murky. Best used as a backup rather than a primary method.