For people, water is the most important substance after oxygen. In adults, 60% by weight is water. The proportion of water in children is even greater, reaching nearly 80%. If a person doesn't eat, depends on the nutrients stored in his body or consumes his own tissues, he can live for a month. But if you don't drink water, it will be difficult for a week. Water loss in the body 10% is a threat to health. If you lose 20% water, your life will be in danger, which shows the importance of water to life.

Water is not only the main component of human body, but also has many physiological functions. The solubility of water is very strong, and many substances can be dissolved in water and dissociated into ionic states, which plays an important role. Insoluble egg protein and fat can be suspended in water to form colloid or emulsion, which is convenient for digestion, absorption and utilization; Water directly participates in the redox reaction in human body, promoting various physiological and biochemical reactions; Without water, it is impossible to maintain physiological activities such as blood circulation, breathing, digestion, absorption, secretion and diarrhea, and metabolism in the body cannot be carried out; Water has a large specific heat, which can regulate body temperature and keep it constant. When the outside temperature is high or the body generates a lot of heat, evaporation and sweating of water help to dissipate heat. When the weather is cold, mountains have great potential to store heat in water, so that the human body will not be cooled by the cold outside, and the water has great mobility. On the one hand, it can transport oxygen, nutrients, hormones and so on. On the other hand, it can excrete metabolites and toxic substances through defecation, urination and sweating. Water is also a self-contained lubricant in the body, such as skin moisturizing. Tears, saliva, joint capsule and serous cavity fluid are all lubricants for corresponding organs.