Water facilitates all of the body's workings at a cellular level.
An inadequate amount can cause fatigue, flushed skin, loss of appetite, light-headedness and dark urine, all warning signs of severe dehydration, says Dulan. People who exercise need to be especially diligent, says Dulan. An adult should drink one to two cups of water prior to exercising, another one to two cups twenty minutes before exercising and half cup to one cup of water every twenty minutes during exercise. People get into trouble when they don't make a conscious effort to drink water, waiting instead to become thirsty.