Osprey Manta 34

Osprey says:
The perfect companion for your next hut-to-hut, the Manta 34 is a premium hike hydration pack you'd be remiss to leave behind. A long day on the trail calls for proper hydration and an included 2.5-liter reservoir makes sure you don't go thirsty. The Manta's lightweight, open mesh AirSpeed backpanel delivers superior ventilation, an improved adjustable torso design provides you with a first-rate fit, and an integrated raincover ensures everything stays dry. A spacious main compartment holds everything you need (and maybe a few things you don't) for your next day hike or supported overnight.