What is dehydration? Dehydration is an abnormal condition in which the body's cells are deprived of an adequate amount of water. Water makes up about 70% of the muscles, organs and tissues in the body and is crucial to many of the body's processes. Dehydration negatively affects important bodily functions, including toxin elimination, delivery of nutrients and oxygen to the cells of the body, energy production, and joint lubrication. Severe dehydration affects every body system and can also impact the proper balance of vital electrolytes. Sodium and potassium are electrolytes essential to healthy functioning of the body and critical processes, such as muscle function and a normal heart rhythm. Complications of severe dehydration can be serious and life threatening and include shock, coma and death. Dehydration is categorized as mild, moderate or severe, based on the extent of the body’s fluid loss. Moderate and severe dehydration can be a life-threatening emergency. Infants, children, athletes and the elderly are particularly prone to dehydration and severe complications, although dehydration can occur in any age group or population. Dehydration can be due to conditions that cause the body to lose too much water, such as excessive heat, sweating, low humidity, bleeding, alcohol intoxication, medication side effects, and high elevation. Dehydration can also be caused by not drinking enough water and fluids. Dehydration is also a symptom of a wide variety of underlying diseases, disorders and conditions, such as gastroenteritis (stomach flu), aldosterone deficiency, and type 1 diabetes. Moderate to severe dehydration can be serious and life threatening, as well as a symptom of a serious disease or condition. Seek immediate medical care (call 911) if you, or someone you are with, have serious symptoms of dehydration, such as not urinating or urinating only very small amounts of dark-colored urine; weakness and dizziness; a change in consciousness or alertness; or severe, persistent diarrhea or vomiting.