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It’s nice to shed weight from a heavy climbing pack by grabbing water on the go. The Flex marries LifeStraw’s light, easily packable water-filtration straw with a collapsible water bottle, a union that’s perfect for both front-country and backcountry climbing. (You can also screw the straw into a hard-plastic bottle, or pair it with a gravity filter or hydration bladder.) You can sip directly from a water source with the straw or fill the bottle and drink from it later at the cliff. I used the Flex in the Flatirons, Colorado, where the fresh, cool water from a snowmelt stream tasted divine both at the source and between burns on my project (from the bottle). But the best part was knowing the water was so safe to drink: The LifeStraw filters away nearly 100 percent of protozoa and bacteria, as well as heavy metals, organic chemicals, and microplastics, with no funky chemical aftertaste.