If you notice that your urine is dark yellow, or if you feel other symptoms of mild dehydration (dryness of the mouth, headaches or dizziness), you probably need more water.
Severe dehydration can make your pulse weak and cause rapid breathing, convulsions, loose skin and sunken eyes. Untreated dehydration can eventually lead to heart failure and death.
What happens to the body if it is not hydrated?
If you notice that your urine is dark yellow, or if you feel other symptoms of mild dehydration (dryness of the mouth, headaches or dizziness), you probably need more water.
Severe dehydration can make your pulse weak and cause rapid breathing, convulsions, loose skin and sunken eyes. Untreated dehydration can eventually lead to heart failure and death.
http://curiosity.discovery.com/question/why-people-need-water