Whoever came up with the idea of carrying potable water within your backpack is or was a genius, that's all we have to say on the matter. Other than that you can make sure that you're kept hydrated the whole day long with clean and safe water with one of these backpacks from such great brands as Osprey and Camelbak.
Osprey Packs Manta 20 AG Hydration Pack 201
Osprey Packs Manta 20 AG Hydration Pack 202
Osprey Packs Manta AG 36 Backpack with Reservoir 189
Osprey Packs Women's Mira AG 26 Backpack with Reservoir 212
Osprey Packs Manta AG 28 Backpack with Reservoir 195