[best for groups]
Why pump when gravity pulls? For groups of four or more, there’s no easier way to treat water, and the GravityWorks is faster, lighter, and more reliable than similar systems. Scoop up two liters of water into the zipper-lock bladder marked “dirty,” then hang it on a tree or rock. Water passes through the hollow-fiber filter (the same used in the HyperFlow) and into the “clean” reservoir.
It only takes about a minute and a half with clear water. It kept six hikers hydrated in Idaho’s panhandle for a week and saw no drop-off in performance or speed. Only gripe: It lacks an adaptor to attach to other bottles or reservoirs (besides the included bladders, it only attaches to 28-mm screw tops like those found on soda bottles), but you can drop the outlet hose end into any vessel. Eliminates: protozoa (including crypto) and bacteria. $100; 14 oz.; cascadedesigns.com
Watch our photo slideshow on how to use a basic gravity filter.