Every day you lose water through your breath, perspiration, urine and bowel movements. For your body to function properly you must replenish its water supply by consuming beverages and foods that contain water.
So how much fluid does the average, healthy adult living in a temperate climate need? The U.S. National Academies of Sciences, Engineering, and Medicine determined that an adequate daily fluid intake is:
About 15.5 cups (3.7 liters) of fluids a day for men
About 11.5 cups (2.7 liters) of fluids a day for women
These recommendations cover fluids from water, other beverages and food. About 20% of daily fluid intake usually comes from food and the rest from drinks.
You've probably heard the advice to drink eight glasses of water a day. That's easy to remember, and it's a reasonable goal.
Most healthy people can stay hydrated by drinking water and other fluids whenever they feel thirsty. For some people, fewer than eight glasses a day might be enough. But other people might need more.
You might need to modify your total fluid intake based on several factors:
Exercise. If you do any activity that makes you sweat, you need to drink extra water to cover the fluid loss. It’s important to drink water before, during and after a workout. If exercise is intense and lasts more than an hour, a sports drink can replace minerals in your blood (electrolytes) lost through sweat.
Environment. Hot or humid weather can make you sweat and requires additional fluid intake. Dehydration also can occur at high altitudes.
Overall health. Your body loses fluids when you have a fever, vomiting or diarrhea. Drink more water or follow a doctor’s recommendation to drink oral re-hydration solutions. Other conditions that might require increased fluid intake include bladder infections and urinary tract stones.
Pregnancy or breast-feeding. Women who are pregnant or breast-feeding need additional fluids to stay hydrated. The Office on Women’s Health recommends that pregnant women drink about 10 cups (2.4 liters) of fluids daily and women who breast-feed consume about 13 cups (3.1 liters) of fluids a day.