Sure this one's easy.  during the day when the air is warm, the air holds water in a gas like state called humidity.  When the air cools, it is no longer able to hold the water (humidity) and therefore, deposits it on the ground as water

 The process that graystripe mentioned is the same process that could save your life if lost in the desert, woods or anywhere. If hiking or nature seeing, always bring a peice of slafane with you. Should you get lost, get some rocks and make a small circle with them, place the selafane over then pushing down in the center and holding the edge with other rocks or what ever you can find that will allow you to create a cone shape with the selafane. The next morning you'll have something to drink. I know i didn't answer your question but i thought you could try it in an experiment.