No sure where alex is from but a friend always takes his "Beast" 6L bladder on hikes with no water sources plus a few bottles. We live in he Desert SW so a lot of the places we hike water sources are unreliable early in the season to non existent by late summer. Ive seen a stream by running good one weekend and a few weeks later bone dry.

Hiking in the Guadalupe Mtns (which by some slim chance you actually find water, your asked to leave it for the wildlife)your advised to carry a gal of water per day... so 2 gals on an overnight. I usually get by with 6L on those hikes but because its only about 4-6miles tops. If I were to hike farther I would need the Gal/day.