In the body, water is the fluid where all life processes take place. This includes carrying nutrients and waste products through the body, maintaining the structure of large molecules like protein and glycogen, and participating in metabolic reactions. Water also serves as the universal solvent for vitamins, minerals, amino acids, glucose, and other small molecules in order to participate in metabolic reactions. Water acts as a lubricant and cushion for joints, inside the eye, the spinal cord, and the amniotic sac surrounding the fetus in pregnancy. It also aids in the regulation of normal body temperature and maintaining blood volume.
Changes sensed by the mouth, hypothalamus, and nerves tell our brains that we are thirsty and require more water. Drinking fluids and nearly all foods contain water. Fruits and vegetables are 90% water in most cases. Meats are usually 50 %. Water also comes from metabolic processes within the body as an end product when energy-yielding nutrients are digested.
Water is produced as an end product when metabolic processes oxidization of these nutrients (such as carbohydrates, proteins, and lipids) through condensation reactions. When these nutrients are broken down, two products remain carbon and hydrogen, these combine with oxygen in order to create CO2 and H2O.
Our bodies must release about 2 cups of water every day as urine in order to fulfill the obligatory water excretion. This is enough to carry away all waste products generated by metabolic processes. This is the minimum amount, anything over this is determined by the activities and intake of the individual. The excess water is lost through the lungs as vapor, The kidneys produce more urine, the skin produces sweat, and some is excreted through feces.