By Alan Kesselheim

Every so often a piece of gear comes along that feels like a breakthrough. The gravity-feed microfiltration system by Platypus has that feeling. It is truly simple, truly convenient, and truly efficient. No more teetering on a streamside rock, keeping the straw in deep water, and laboring over a pump. Gravity does the job for you. Fill the bag with dirty water, hang it from a tree branch, and let it drain down through the filter into a water bag or bottle. Works like a charm, filters the usual 99.9% of bad juju, and leaves you free to eat lunch or relax. That's it. And don't relax too long, because it filters 1.5 liters a minute. The only minor hitches I've experienced are that the clip that pinches off water flow between filling bottles doesn't always completely seal (just loop the tube through the handle if it drips), and sometimes the hose needs to be 'burped' at the beginning to release air bubbles and get the flow going. If the flow is too slow, backflush the GravityWorks by raising the bottle above the bag and back down a few times. In a few seconds you'll see the air bubbles escaping into the reservoir and you're good to go.

GravityWorks Intel: 2.0 liter and 4.0 liter options, 7 oz. and 11 oz., $109.95 – $119.95.

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