Although deficiencies of energy or nutrients can be sustained for months or even years, a person can survive only a few days without water. Experts rank water second only to oxygen as essential for life. In addition to offering true refreshment for the thirsty, water plays a vital role in all bodily processes. It supplies the medium in which various chemical changes of the body occur, aiding in digestion, absorption, circulation and lubrication of body joints. For example, as a major component of blood, water helps deliver nutrients to body cells and removes waste to the kidneys for excretion.