The document discusses dehydration, which is an excessive loss of water from the body, usually through sweating, urination, or evaporation. On a normal day, the body loses about 2.5 liters of water through urine, feces, and perspiration. Causes of dehydration include diarrhea, vomiting, fever, certain medications, and not drinking enough water. Signs of dehydration are increased thirst, dry lips, dry and warm skin, rapid weight loss, weakness, and fever. Prevention involves drinking plenty of fluids and eating foods high in water to replace lost fluids.