I don't know what would happen after a month, but David Blaine stayed underwater for a week. In 2006, David Blaine performed a spectacular stunt in which he submerged himself in a water-filled sphere about 2.5 meters in diameter for seven days. To avoid needing to use the toilet during this time, he fasted for 48 hours before the stunt began, but used a catheter to relieve himself. His only nutrition consisted of a liquid diet administered through a feeding tube—comprising Gatorade, Pedialyte, and water.
After the week, he developed numerous health problems. Prolonged exposure to water caused his skin to become extremely wrinkled and begin to peel. This condition, known as "trench foot," occurs when skin remains wet for extended periods. Blaine's blood vessels constricted as a physiological response to the weightless environment, reducing his blood plasma volume to 75% of normal. This reduced blood flow throughout his body and led to damage to his liver and kidneys. He also described sharp, stabbing pains throughout his body, followed by a gradual loss of sensation in his extremities.