Clean water is non-negotiable on a backpacking trip, and the filter you choose affects your weight, your time at water sources, and how easily you can treat water for a group. Squeeze filters and pump filters both remove bacteria and protozoa, which are the main biological risks in most backcountry water, but they work differently and suit different hikers. Neither type removes viruses reliably on its own, so in areas where viruses are a concern, pair filtration with purification tablets or ultraviolet treatment.

A squeeze filter is a small hollow-fibre cartridge that you attach to a soft bottle or reservoir and squeeze to push water through, and it is the most popular choice among ultralight hikers for good reason. The whole system weighs around two to three ounces, has no moving parts to break, and is fast enough for one or two people filling bottles at a stream. Its weaknesses are clogging in silty or murky water and the hand strength needed to squeeze a full litre, which can be tiring after a long day.

A pump filter uses a hand pump to push water through a cartridge into your bottle or reservoir, and it is heavier, usually around ten to sixteen ounces, but it handles difficult water far better. The pump lets you draw from shallow pools, muddy sources, and awkward spots where a squeeze bottle cannot reach, and a pre-filter keeps much of the silt out of the cartridge. For groups, for desert hiking with poor sources, or for anyone who struggles with grip strength, a pump is often worth the extra weight.

Flow rate and maintenance are where the two systems really differ in daily use. A new squeeze filter flows quickly but slows as it clogs, and backflushing with clean water, using the syringe or a backflush attachment it comes with, usually restores much of the flow. A pump filter also slows with use, but its cartridge can often be cleaned in the field by scrubbing or rinsing, and the pump mechanism itself needs occasional lubrication and seal checks. Whichever system you choose, practise backflushing or cleaning at home before the trail.

Capacity and group size should drive the decision more than headline weight. A solo hiker filtering a litre or two at a time will be happy with a squeeze filter, while a group of four filtering eight litres at camp will find a pump, or a gravity system, much less tedious. Gravity filters, which hang a dirty-water bag above a filter and let gravity do the work, are a good middle ground for groups and base camps, because they filter large volumes while you set up camp, though they are slower and need a place to hang.

Cold weather and freezing deserve special attention, because a hollow-fibre filter that freezes can crack internally and stop protecting you, even if it still flows. In freezing conditions, keep the filter in your sleeping bag at night and in a warm pocket during the day, and never let it freeze with water inside. Ceramic pump filters tolerate cold a little better, but they are heavier and more fragile, so the habit of protecting your filter matters whichever type you carry.

To choose, think about your typical water sources, your group size, and how much weight you are willing to trade for convenience. For most solo three-season hikers, a squeeze filter plus purification tablets as a backup is the lightest reliable system. For groups, murky water, or shallow desert sources, a pump filter earns its weight. Either way, always have a backup method, know how to maintain your filter, and treat water every time, because the clearest-looking stream can still carry something you cannot see.