Drinking enough water is important to our health. If we want to operate at our highest level and feel great both mentally and physically, we need to stay hydrated throughout the day. But often … we don’t. People may go through their days dehydrated and not even know it. Dehydration can make you sick. Extreme dehydration can lead to death. However, many side effects of dehydration are not life-threatening. But they can still affect your health. In fact, you may be suffering from some of these side effects without knowing that dehydration is the cause. First, what is dehydration? Dehydration happens when you use or lose more fluid than you take in. Your body doesn't have enough water and other fluids to carry out its normal functions. On the U.S. Geological Survey Water Science School website, experts explain how much of our bodies are made of water.