Approximately 73 percent of the average human brain is composed of water. The heart is also composed of 73 percent water, while the lungs are 83 percent water. The average human adult body is made up of 60 percent water.
In order to survive, the average adult must consume 2.2 to 3 liters of water daily. Water provides several necessary functions in the human body. It regulates the body's internal temperature through perspiration and respiration and flushes waste, mainly through urination. Water also acts as a lubricant to the joints as well as a shock absorber for the brain, spinal cord and fetus.