From WebMD: “Dehydration is a condition that occurs when the loss of body fluids, mostly water, exceeds the amount of water that is taken in. With dehydration, more water is moving out of our cells than is moving in.”
Water is continuously lost from our body through various routes, via the lungs through evaporation when breathing, the gastrointestinal tract in feces, the skin through evaporation and perspiration, and of course through the kidneys in our urine.
Depending upon age, weight, body composition and other variables, the human body may be composed of approximately 50-75% water.
People begin to experience impairment in mental abilities and coordination with only a 1% loss of body water, while feelings of thirst typically occur when 2-3% of body water is lost.