What's the difference between a pump water filter and a gravity or straw filter?

A pump filter uses a hand-operated piston or lever to force water through a cartridge, giving you control over flow rate and the ability to draw from shallow or hard-to-reach sources. Gravity and straw systems are lighter and simpler but rely on a head of water or direct sipping, which is slower for filling bottles and harder to use from a thin trickle. Pumps are favored when you need to fill multiple containers or work from shallow water.