Rehydration is the replenishment of water and electrolytes lost through dehydration. It can be performed by oral rehydration therapy (drinking an electrolyte solution) or by intravenous therapy (adding fluid and electrolytes directly into the blood stream).
As oral rehydration is less painful, less invasive, less expensive, and easier to provide, it is the treatment of choice for mild dehydration from infectious gastroenteritis. Because severe dehydration can rapidly cause permanent injury or even death, intravenous rehydration is the initial treatment of choice for that condition.
If someone is sufficiently dehydrated that he or she exhibits the signs of moderate to severe dehydration, medical attention should be sought.