An adult needs to drink about 1.5 liters of water every day in addition to eating. When people are in a difficult situation, such as getting lost in the desert or being trapped under debris during an earthquake, they can survive without food for several days as long as they have water to drink, thereby gaining precious time to wait for rescue. Why do people need to drink water? What important role does water play in human life?
Water is an important component of the human body. The water content in an adult's body accounts for about 60% of their body weight; the higher the age, the higher the percentage of water in the body. The water content in a newborn baby's body accounts for about 75% of their body weight. Two-thirds of the total body fluid is distributed in cells, accounting for about 40% of body weight.
Human life activities cannot do without water for a moment. An adult secretes a total of 6-8 liters of digestive fluids every day, of which about 99% is water. This is because food is ultimately broken down into absorbable small molecule nutrients in the small intestine, and water serves as a medium for enzymes in digestive fluids. After digestion, small molecule nutrients also need to be dissolved in water before being transported and crossing the small intestinal wall into the bloodstream. More than half of human blood is water, and small molecule nutrients need to be dissolved in blood before being transported to various parts of the body. Metabolic waste products produced by cells throughout the body also need to be diffused into the bloodstream before being excreted by excretory organs. The human body constantly excretes water. The kidneys are the main excretory organs of the human body. The kidneys convert metabolic waste products in the blood along with excess water into urine. Because dissolving these metabolic waste products requires a large amount of water, urine is mostly water. Normal people excrete 1-2 liters of urine every day. During intense physical labor or intense exercise, or in hot weather, the body temperature rises, and the body often sweats to dissipate heat, with about 99% of sweat being water.
People can go without eating for several days because the human body stores a certain amount of fat and glycogen, and the body can rely on consuming these stored energy substances to maintain life activities. In extreme hunger situations, the body can also obtain energy by consuming the structural proteins that make up the human body. However, the human body is always in a state of water balance, that is, water is not stored in the body. Without food or water, the body still excretes a certain amount of urine every day because metabolism is still ongoing. When the daily urine output is only 0.4-0.5 liters, metabolic waste products cannot be completely excreted from the body, which will accumulate and cause harm to the human body and disrupt the normal functioning of the body. If the human body loses 20% or more of its water, it will lead to circulatory dysfunction and endanger life.