Filters

A straw is the smallest and cheapest, but you drink straight from the source and cannot get water into a bottle. A bottle with a built-in filter combines both and is suitable for regular trips. A pump draws water even from a shallow puddle and fills quickly, in exchange for manual effort. A gravity system hangs on a branch and fills several bottles unattended, making it the winner for groups and at camp. For winter, bear in mind that a frozen filter will crack.