No matter how many times your Apple Watch reminds you to get up to refill your glass water bottle and do a lap around the office during the day, and regardless of whether you prefer the soft mouthfeel of Evian to the crisp neutrality of Poland Spring, the human body is, and always will be, composed of more than 50% water . Consuming ample H2O on a daily basis is so much more than just a bragging right ; it is essential for sustaining life, for powering your brain (73% water), your muscles (79%), and, perhaps most importantly, your skin (a healthy 64%).