Your body contains more water than any other substance, using it in all the cellular processes you need to maintain optimal health. Water also serves to absorb heat from your body as a means to regulate your temperature. The amount of water in your body depends on such factors as your body composition, your state of health, your activity level and your environment. When you drink water to replenish your fluid stores, the amount you retain depends on how much water your body currently holds for the condition you are in.
Fluid balance refers to the amount of liquid you consume compared to how much your body needs. You take in liquid from the beverages you drink as well as from the foods you eat, such as fruits, vegetable and soups. Your body loses fluid through sweat, evaporation, respiration and evacuation through urination and bowel movements. If you are ill, you may lose additional fluids through vomiting or diarrhea. When your liquid intake is low, your body regulates your fluid balance by decreasing your sweat and urine output. Conversely, if you drink more than your body needs, your urine output increases.
When your body is in a state of optimal hydration, the amount of fluids you take in matches what you lose through your skin, lungs and kidneys. Therefore, if you drink 8 ounces of water while you are well hydrated and in a comfortable environment, you will excrete the majority of this extra water in your urine, with small amounts also being lost in your exhalations and through skin evaporation. In other words, your body retains very little additional water if you already are fully hydrated.
In dehydration, your body needs more water than it currently holds. Dehydration occurs either because your fluid intake is low or because your fluid loss is elevated for reasons including a hot environment, increased physical activity or illness. In a state of dehydration, your body conserves water by minimizing urine production and decreasing perspiration. These actions, however, prevent your body from its normal functions of excreting waste products and regulating your body temperature. When you drink 8 ounces of water while you are dehydrated, your body retains this water to help restore fluid balance and maintain normal physiological functions.
By the time you feel thirsty, you are already on your way to dehydration, cautions the Centers for Disease Control and Prevention. It is especially important to consume sufficient fluids while you are in the sun, on hot days and while engaged in strenuous physical activity. If you urinate less frequently than usual and your skin is dry, you may need to drink more water. Additionally, your body may also retain extra fluid in response to hormones, heat or high salt intake. In these cases, consuming extra water may ease your symptoms. However, consult with your health care provider if you notice any unexplained swelling in your body.