Humans have developed an incredible automatic defense system over the past couple million years. All the things that we need for our survival is pretty much on auto pilot. When we are running low on fuel, all we think about is eating. When are low on fluids, we can't spend more than a couple seconds without thinking about drinking. When something threatens us, we get a sudden burst of energy so that we can either fight, or run away. Despite how amazing these systems are, we also have the capability to ignore them to some degree. And when we do this, it's usually a bad thing.
When you don't drink enough water, you become dehydrated. Once in a while is not such a big deal, because you can always make up for it later. But consistent dehydration can lead to several adverse health conditions that you don't want. Most people wait until they are thirsty before they drink, but this is actually too late. A feeling of thirst is actually a warning sign that you are getting dangerously low on water.
Several studies have shown that consistent dehydration leads to a much less efficient immune system. This means you'll get sick more often, and when you do get sick, it will last longer, and be more severe. With constant hydration, you can improve your immune system and stay healthy. Also, drinking plenty of fluids while suffering from common colds has long been considered an effective way of shortening the duration of the illness.
One more danger of not getting enough fluids is excessive tiredness. When your body is dehydrated, it takes much more energy for your body to perform it's daily tasks, which will make you tired. Sometimes it can feel as if you are not getting enough sleep, when in reality you are just dehydrated. In order to give yourself some more energy, consider drinking a few more glasses of water a day.
Dehydration has also been linked with excessive hunger. Often times we eat when we think we're hungry, but we're really not. While this is usually due to some psychological trigger, being dehydrated is actually a physical cause of pseudo hunger. The stomach feels empty,and naturally you feel like eating something. But if you were to drink a full glass of water instead, you'll find that the hunger pains can easily vanish.
Lastly, without sufficient water flushing through your system on a regular basis, you can build up free radicals. These are chemicals that are naturally byproducts of your normal metabolism. If you drink enough water, they are simply flushed out, and there's no problem. But without enough water, these can build up over time and cause some serious problems.
It's apparent that not drinking enough water is a source of many problems. By drinking a few glasses of water a day, you can avoid most of these problems and live a much healthier life.