There is no one answer to the question of how much water is significant. We each need a different amount, depending on our size, body composition, and activity level as well as the temperature and humidity of the environment. Over the course of a few hours, body water deficits can occur as a result of reduced intake or increased water losses from physical activity and environmental (heat) exposure. However, on a day-to-day basis, fluid intake, driven by the combination of thirst and the consumption of food and beverages at meals, allows maintenance of hydration status and total body water at normal levels. The Adequate Intake (AI) for total water, including drinking water, beverages, and food, is 3.7 liters per day for men and 2.7 liters per day for women. Intake recommendations are higher during pregnancy (3.0 liters per day) and lactation (3.8 liters per day). Activity and sweating increases water needs, so athletes and active people need much more water, especially if they work and train in warm, humid climates. Water intake comes from a combination of drinking water, beverages, and the water in foods. Approximately 81 percent of our total daily water intake comes from beverages, with the remaining 19 percent from foods. Some foods, such as fruits and vegetables, contain a substantial amount of water, whereas others-grain products, for example-provide very little. Our bodies also produce a small amount of water (about 250 to 350 milliliters per day) in metabolic reactions.