Survival skills
A human being can survive an average of three to five days without the intake of water. The issues presented by the need for water dictate that unnecessary water loss by perspiration be avoided in survival situations. The need for water increases with exercise.
NEEMO
NASA has used it since 2001 for a series of space exploration simulation missions, usually lasting 7 to 14 days, with space research mainly conducted by international astronauts. The mission had cost about 500 million U.S. dollars. 
The crew members are called aquanauts (as they live underwater at depth pressure for a period equal to or greater than 24 continuous hours without returning to the surface), and they perform EVAs in the underwater environment. A technique known as saturation diving allows the aquanauts to live and work underwater for days or weeks at a time. After twenty four hours underwater at any depth, the human body becomes saturated with dissolved gas. With saturation diving, divers can accurately predict exactly how much time they need to decompress before returning to the surface. This information limits the risk of decompression sickness. By living in the Aquarius habitat and working at the same depth on the ocean floor, NEEMO crews are able to remain underwater for the duration of their mission.