Your body needs more fluid in several common situations that raise dehydration risk. According to the U.S. Centers for Disease Control and Prevention (CDC), people typically need more water when they are in hot climates, more physically active, running a fever, or having diarrhea or vomiting.
Those conditions increase fluid loss through sweat or illness, so intake has to rise to keep temperature regulation, joints, and waste removal working normally. CDC also notes that daily water needs vary by age, sex, pregnancy or breastfeeding status, and activity level—and that infants, young children, and adults 65 and older are among groups that need extra care around heat and hydration.