This is why you don't go hiking without preparing:
A teenager called for help on the PCT when he ran out of water supply and knew that he would soon be totally dehydrated and lost. Read the full story here, but really, all there is to know is that he was unprepared and couldn't find water.
Before you hit up ANY trail, you need to be sure that you know where the water supplies are, how the water supplies are as far as quantity, and be aware if any droughts are going on (as there are currently in California). Don't be an idiot.