If you've exhausted all of your personal water supplies, sometimes you have to get creative with water in an emergency. One way to collect water is using a solar still. Most often, you will already have the supplies to make one on hand.
a) Dig a large, shallow hole (4' wide - 3' deep).
b) Put a collection container in the middle of the hole.
c) Place a piece of 6' x 6' clear plastic over the hole.
d) Put a small rock or something right in the middle of the plastic that causes the plastic to slope to the container.
e) Wait for water to condense on the plastic and drip into the collection container.
Detailed Instructions: http://www.desertusa.com/mag98/dec/stories/water.html