During the time when you are not drinking water, you still lose some water to sweating and urine. Especially in hot climates, sweating is an important function of the body to maintain the body temperature in the desired range. If this water is not replaced, the body gets dehydrated. This induces a reaction which reduces the activity of the "body thermostat", in order to tolerate a higher body temperature without excessive sweating. This, in turn, helps to maintain the fluid balance of the body.
When you start drinking again after this the dehydration period, the body starts sweating to regulate the body temperature again, since the loss of water is no longer critical. For a detailed discussion, including further references, please see:
