Charles W. Bryant,

HOW STUFF WORKS, You've heard the phrase and probably even said it yourself -- ""I'm dying of thirst."" This common expression that means you're in need of a cool beverage becomes literal when you're faced with a survival scenario. Dehydration can kill you, which is why finding clean drinking water is at the top of the list when you're fighting for your life. Humans can only survive for a few days without water, and in hot, arid conditions, dehydration can set in within a few short hours.

Beyond Parched

Dehydration goes far beyond thirst. Each and every cell and organ in your body needs water to function, so going without it for more than a few days can kill you. Hot conditions make matters worse because of water loss through perspiration, but we lose water in more ways than just sweat. You also lose it through your feces, urine and even your breath.

The Downward Spiral

There are three stages of dehydration. During the first stage, you'll develop a serious case of ""cotton mouth."" You'll also pee less frequently, with decreased output, and your urine will have a deep color and strong odor. During the next stage, you'll urinate even less, your eyes will become dry and sunken, and your heart rate will increase. You know your dehydration is severe when you stop peeing completely, become lethargic and irritable, and you're overcome with nausea. Vomiting may also be in the cards, which will dehydrate you even more. If you fail to rehydrate once your situation becomes severe, you could fall into shock and die.

Hydration Station

Once you find some water, drink it slowly, but steadily. Drinking too fast may increase your nausea. Stay away from alcohol and caffeine -- they'll just make you more dehydrated by increasing your urine output. If you're stranded on a desert island or stuck in a life raft in the ocean, stay away from the salt water. Drinking it will also cause you to become more dehydrated. You know you're in the clear when your nausea decreases, your energy increases, and your urine becomes clear and frequent. If you're going on an outdoor adventure, put some money into a good water filter before you go. This way any creek, river or lake can provide you with drinkable water.