Nalgene all the way.

Last year I went on a two-day, 20 mile hike about four hours from home. I had a 3 and a 2 liter water bladder in my backpack. Somewhere along the drive the 3L bag leaked, soaking my gear with about 2L of water. The ground water where I was hiking is highly contaminated with naturally-occuring arsenic and mercury, so boiling it wouldn't have made it safe.

Luckily, being the paranoid type I had two 1L Nalgene bottles filled with water along just in case (along with several liters of bottled water). The hike went off without a problem.

Now my water bladders are just used for extra weight on the treadmill.

-Blast