I am also a big fan of the hydrapak.
No sloshing like a nalgene and it compresses and packs easily when not being used so I don’t have to carry a full sized empty container around.
Stash™ 750 ML - Flexible Water Bottles - Products | HydraPak
<p>Welcome to utility and design in harmony. Essential equipment for every adventurer, the Stash 750 flattens for maximum room in your pack. Expands for use on the trail. It’s compact, flexible and 50% lighter than a hard bottle. Construction with purpose
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