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.
Salt poisoning
Although humans cannot survive on seawater alone—and, indeed, will sicken quickly if they try—some people have claimed that up to two cups a day, mixed with fresh water in a 2:3 ratio, produces no ill effect. During the 18th century, British physician Richard Russell (1687–1759) advocated the practice as part of medical therapy in his country. In the 20th century, René Quinton (1866–1925), in France, would also endorse the practice. Currently, the practice is widely used in Nicaragua and other countries, supposedly taking advantage of the latest medical discoveries.) In his 1948 book, "Kon-Tiki", Thor Heyerdahl reported drinking seawater mixed with fresh in a 2:3 ratio during the 1947 expedition. The French physician Alain Bombard (1924–2005) survived an ocean crossing (1952–53) in a small Zodiac rubber boat using mainly raw fish meat, which contains about 40 percent water (like most living tissues), as well as small amounts of seawater and other provisions harvested from the ocean. His findings were challenged, but an alternative explanation was not given. A few years later, an American sailor and adventurer, William Willis (1893–1968), claimed to have drunk two cups of seawater and one cup of fresh per day for 70 days without ill effect when he lost part of his water supply.