Dehydration occurs when the body loses water, or when the intake of water does not meet demand. Dehydration is caused by any condition that leads to water loss.

Conditions that cause water loss include:

• Burns
• Diarrhea
• High fever
• Heat illness
• Drug side effects:
• Diuretics
• Loop diuretics
• Thiazide diuretics
• Infections:
• Gastroenteritis
• Influenza
• Pneumonia
• Urinary tract infection
• Tonsillitis
• Intense exercise
• Poor water intake
• Vomiting

Water makes up about 60 percent of the body's weight. Water is required to keep the body functioning normally. An average size adult requires about 1 quart of water per day. Physically active adults may require 4 to 5 quarts per day. In addition to water, the body requires salts, which are dissolved in water. Body salts include sodium, potassium, magnesium, calcium, and chloride. The kidneys regulate water and salt balance carefully.