A person must drink water to survive. Up to 60 percent of an adult human’s body consists of water, and generally a person needs to drink 2 to 3 liters of water per day.
Water plays a critical role in proper cell function, internal body temperature regulation and body waste regulation. Water serves as a shock absorber and lubricant for the brain, nerves and joints. The water in the blood transports nutrients throughout our body and carries excess heat via sweat away from our body.
While it’s possible for a human to go for a week without water, a person can usually survive only three to four days without water. Hotter temperatures, increases in activity and direct sunlight increase the frequency that humans need to drink. Foods can provide water, but the best source for hydration is water itself. Milk, soup and juices are also excellent ways to obtain water. Any drink with caffeine is not ideal, because the caffeine interacts with human body chemistry to release water.
Water makes up about 78 percent of a baby's body and 65 percent of a 1-year-old child. Adult men clock in at about 60 percent water, and women are around 55 percent. Even human bones have about 31 percent water content.