The excess amount of water in our body come out by means of sweat
We sweat when their is a difference of temperature between our body and the atmosphere.When we run or perform any other physical exercise our gets heated  up due to friction in our body parts.Thus having the temperature of the atmosphere lower than our body ,the water present in our body is hot and comes out to balance the temperature between the atmosphere and our body.Thus the heat flows from hot body to cold body until they have equal heat energy,thus following this principle heat from body travels to air touching the body surface until they both have equal heat energy. When the temperature is equal we don't  perspire.