The Facts

Two-thirds of the human body is made up of water. That means that if a person weighs about 70 kilograms (154 pounds), their body contains about 46 litres of water. Almost 70% of this water is inside the body's cells, 20% is in the space surrounding cells, and slightly less than 10% is in the bloodstream. The water in the human body is essential to keeping it healthy.

When the amount of water you intake matches the water you excrete, the body's water supply will be balanced. If you are healthy and do not sweat excessively, you should drink at least 2 to 3 litres of fluid a day (about 8 glasses of water) to maintain your water balance and protect against the development of kidney stones.

Dehydration results when there is a deficiency in the body's water supply. If the brain and kidneys are functioning properly, the body will be able to manage minor changes in water intake. It's usually possible to drink enough water to make up for any water loss. However, it may be difficult to drink enough water if you are vomiting, have severe diarrhea, are exposed to excessive heat, or have a fever.

Dehydration is common among seniors, infants, and children. Seniors sense thirst more slowly so they may not recognize that they are becoming dehydrated and not drink enough fluids. Infants and young children lose more fluid during diarrhea or vomiting than older children and adults.

Some dehydration is relatively mild; however, severe loss of the body's supply of fluids can be potentially life-threatening. When the body's supply of fluids falls below a certain amount, a condition called hypovolemic shock may result.


Some of the conditions that can result in extreme fluid loss are:

Gastroenteritis: If the gastrointestinal tract becomes infected or inflamed by a virus or bacteria that results in vomiting or severe diarrhea, dehydration may develop. Gastroenteritis usually does not last for more than 36 hours.

Cholera: Consuming water or foods that have been contaminated by human wastes infected with the cholera bacterium will cause vomiting and severe diarrhea and can lead to dehydration, hypovolemic shock, and, in some cases, death.

Excessive use of certain medications: Diuretics, also known as "water pills," stimulate the body to increase the rate and volume of urination and the loss of electrolytes (dissolved mineral salts such as sodium, potassium, and chloride) in the urine. Although problems are uncommon when diuretics are used and monitored properly, overuse combined with a low-salt diet may cause dehydration.

Bulimia: Bulimia nervosa is an eating disorder that involves uncontrolled or compulsive binge eating. Most often, the condition also involves purging through self-induced vomiting, laxatives, enemas, diuretics, or excessive exercising. All types of purging can result in dehydration.

Addisonian crisis: The adrenal gland, a gland located above the kidneys, produces steroid hormones that are involved in keeping the body's water in balance. Although it's rare, the adrenal gland can fail, causing a disease called Addison's disease, which can result in excessive loss of urine, leading to dehydration.

Symptoms and Complications

The body will attempt to deal with dehydration by first stimulating the thirst centres of the brain, which will prompt someone who is dehydrated to drink more fluid. However, if water intake cannot keep up with water loss, dehydration will become severe and the body will respond by doing things that decrease the loss of water, such as decreasing sweat and producing less urine. People who are adequately hydrated will usually urinate light-coloured urine every 3 to 4 hours.

Symptoms of mild to moderate dehydration include thirst, reduced sweating, decreased urine production, dry mouth, and reduced skin elasticity.

Because the water in the bloodstream is very important, the water in and around the cells will begin to move into the bloodstream. If dehydration continues, the cells in the body will begin to shrivel and malfunction, and tissues in the body will begin to dry out. Because brain cells are among the most vulnerable to dehydration, confusion and even coma can occur.

With severe dehydration, the body's electrolytes may become deficient, and water will not be able to move as easily from inside the cells out into the blood. The amount of water in the bloodstream will be further decreased and blood pressure can drop, causing lightheadedness or the feeling of starting to faint, particularly when standing up suddenly. If water and electrolyte losses continue, blood pressure can fall dangerously low and result in shock and severe damage to many internal organs, such as the kidneys, liver, and brain.

Dehydration is a serious problem in young children and infants due to their larger skin surface area, and it can occur even after a few hours of vomiting, diarrhea, or profuse sweating.

If a baby is dehydrated, there may be:

  • an absence of tears during crying
  • a dry mouth
  • a sunken soft spot on the top of the head
  • failure to produce a wet diaper after 8 hours

Making the Diagnosis

Dehydration may be suspected in cases of persistent vomiting, diarrhea, or loss of fluid through the urine or the skin. Symptoms associated with severe dehydration include pale, cool, and clammy skin, a weak and rapid heartbeat, a shallow and hurried breathing pattern, and severely low blood pressure. Some people may also be anxious and restless and complain of thirst. Skin on the knees and elbows may be mottled.

Diagnosis of dehydration is usually based on symptoms and physical examination.

Treatment and Prevention

For mild dehydration, drinking plain water may be all you need. However, if both water and electrolyte losses have occurred, electrolytes (especially sodium and potassium) should also be replaced. There are a number of flavoured commercial drinks or oral rehydration solutions that have been formulated to replace the electrolytes (salts) lost during vigorous exercise. These drinks can be used to prevent dehydration or to treat mild dehydration. Just drinking plenty of fluids and consuming a little additional salt during or after exercise will also work. If you have heart or kidney problems, consult your doctor about safely replacing fluids before exercising.

If dehydration becomes worse and if blood pressure drops enough to cause shock or the threat of shock, get immediate medical attention. In these severe cases, an intravenous solution containing sodium chloride is usually given. Intravenous fluids are given rapidly at first, then more slowly as dehydration improves.

The underlying cause of dehydration must always be treated. For example, if diarrhea is the cause, then medications to treat or stop the diarrhea may be necessary as well. Once the cause of dehydration has been treated, monitoring is necessary to ensure that the oral intake of fluids is sufficient to maintain hydration.

If a child has any symptoms of dehydration, a health care provider should be contacted immediately. Dehydration can often be prevented in children by using replacement solutions such as Pedialyte®.

In order to prevent dehydration, drink extra water or commercially available fluid replacements when you encounter potentially dehydrating conditions such as in hot, humid, or cold weather; high altitudes; or when you physically exert yourself. Caffeinated (tea and coffee) and alcoholic beverages should be avoided because they are dehydrating. It is recommended that people drink 2 to 3 litres (about 8 glasses) of fluid every day.


*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.