2.12 Fluid balance
Although a person can survive for several weeks without food, without fluids, someone can survive for only a few days. A loss of water equivalent to just 1% of body weight is enough to make someone feel thirsty and to have an effect on ability to concentrate. Such a loss has been shown in some studies in schools to result in a 10% decrease in the mental performance of children. A 4% loss results in dizziness and reduced muscle power. By the time there is a 6% loss, the heart is racing and sweating ceases and a 7% loss results in collapse and subsequent death, if the loss is not replaced.