Breathing contains a lot of water. We all know that when breathing, human cell activity requires oxygen and emits carbon dioxide and other exhaust gases. But in fact, breathing also discharges a lot of water. According to the 2012 issue of the Polish Journal of Thoracic Medicine and Allergology, people can exhale 17.5 ml of water per hour while sleeping, and the amount of water exhaled during exercise is four times that of sleeping.