Open Question: Water requirements for overnight backpacking trip?

I'm planning on backpacking out to the backcountry in Big Bend National Park, I've only every taken daytime trips before, how much water do you think I should pack out for a one night overnight trip? Also, any other tips about backpacking/hiking Big Bend are appreciated.

Source:
http://answers.yahoo.com/question/index?qid=20101227183747AASHXML

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