Proper hydration is essential to regular bodily function. You can live for weeks without eating, but people tend to keel over within a few days of water deprivation. You don't need to guzzle so much water that you spend half your day in the bathroom, but even so many people go through their days in a state of mild dehydration. This is often because of coffee or alcohol intake - both are actually severe diuretics, and it's very hard to stay well hydrated under their influence.

Water or sports drinks are important to consume before, after and during athletic activity. Going into a workout thirsty leads to a dissatisfying and low intensity exercise experience, with more muscle soreness and less pleasure. It's better to drink moderate amounts at moderate speeds throughout the day than to just chug mass amounts of water when you think you need to. When your throat gets dry, you're already too thirsty. Make sure that you increase your water intake during particularly hot days, especially if you're going to be outside engaged in strenuous activity. Running around in the summer sun without being hydrated can easily lead to death by exhaustion.

Other things that can lead to dehydration are eating too much salty food or eating things that are sugary. Both have a strong dehydrating effect, which is why you should steer away from soda when you're thirsty. The water in the soft drink will give you a temporary feeling that you are hydrating, but then the sugars and salts will drain more liquids from your cells.