The human body, which is made up of between 55 and 75 percent water (lean people have more water in their bodies because muscle holds more water than fat), is in need of constant water replenishment.
Your lungs expel between two and four cups of water each day through normal breathing – even more on a cold day. If your feet sweat, there goes another cup of water. If you make half a dozen trips to the bathroom during the day, that’s six cups of water. If you perspire, you expel about two cups of water (which doesn’t include exercise-induced perspiration).
A person would have to lose 10 percent of her body weight in fluids to be considered dehydrated, but as little as two percent can affect athletic performance, cause tiredness and dull critical thinking abilities. Adequate water consumption can help lessen the chance of kidney stones, keep joints lubricated, prevent and lessen the severity of colds and flu and help prevent constipation.
Health benefits of water
Water is crucial to your health. It makes up, on average, 60 percent of your body weight. Every system in your body depends on water.
Lack of water can lead to dehydration, a condition that occurs when you don’t have enough water in your body to carry on normal functions. Even mild dehydration – as little as a 1 percent to 2 percent loss of your body weight – can sap your energy and make you tired. Dehydration poses a particular health risk for the very young and the very old. Signs and symptoms of dehydration include:
- Excessive thirst
- Dry mouth
- Little or no urination
- Muscle weakness
How much water do you need?
Every day you lose water through sweating – noticeable and unnoticeable – exhaling, urinating and bowel movements. For your body to function properly, you need to replace this water by consuming beverages and foods that contain water. So how much water, or more precisely fluid, do you need?
This isn’t an easy question to answer. A healthy adult’s daily fluid intake can vary widely. Most people drink fluid to quench thirst, to supply perceived water needs and “out of habit.” At least three approaches estimate total fluid (water) needs for healthy, sedentary adults living in a temperate climate.
- Replacement approach. The average urine output for adults is 1.5 liters a day. You lose close to an additional liter of water a day through breathing, sweating and bowel movements. Food usually accounts for 20 percent of your fluid intake, so you if you consume 2 liters of water or other beverages a day (a little more than 8 cups), along with your normal diet, you can replace the lost fluids.
- Eight 8-ounce glasses of water a day. Another approach to water intake is the “8 x 8 rule” – drink eight 8-ounce glasses of water a day (about 1.9 liters). The rule could also be stated, “drink eight 8-ounce glasses of fluid a day,” as all fluids count toward the daily total. Though this approach isn’t supported by scientific evidence, many people use this basic rule as a guideline for how much water and other fluids to drink.
- Dietary recommendations. The Institute of Medicine recommends that men consume 3 liters (about 13 cups) of total beverages a day and women consume 2.2 liters (about 9 cups) of total beverages a day. These guidelines are based on national food surveys that assessed people’s average fluid intakes.
You can choose any of these fluid intake approaches to gauge your fluid needs. But your current total fluid intake is probably OK if you drink enough water to quench your thirst, produce a colorless or slightly yellow normal amount of urine, and feel well.
Factors that influence water needs
You may need to modify total fluid intake from these recommended amounts depending on several factors, including how active you are, the climate, your health status, and if you’re pregnant or breast-feeding.
- Exercise. If you exercise or engage in any activity that makes you sweat, you’ll need to drink extra water to compensate for that fluid loss. Drink 2 cups of water two hours before a long endurance event, for example, a marathon or half-marathon. One to 2 cups of water is also adequate for shorter bouts of exercise. During the activity, replenish fluids at regular intervals, and continue drinking water or other fluids after you’re finished. During intense exercise involving significant sweating, for example, during a marathon, sodium is lost in sweat, and you may need a sports drink with sodium rather than just water.
- Environment. You need to drink additional water in hot or humid weather to help lower your body temperature and to replace what you lose through sweating. You may also need extra water in cold weather if you sweat while wearing insulated clothing. Heated, indoor air can cause your skin to lose moisture, increasing your daily fluid requirements. And altitudes greater than 2,500 meters (8,200 feet) also can affect how much water your body needs. Higher altitudes may trigger increased urination and more rapid breathing, which uses up more of your fluid reserves.
- Illnesses or health conditions. Some signs and symptoms of illnesses, such as fever, vomiting and diarrhea, cause your body to lose extra fluids. To replace lost fluids, drink more water or oral rehydration solutions (Gatorade, Powerade, CeraLyte, others). When water loss can’t be replaced orally, intravenous water and electrolytes may be necessary. Increased water intake is nearly always advised in people with urinary tract stones. On the other hand, you may need to limit the amount of water you drink if you have certain conditions that impair excretion of water – such as heart failure and some types of kidney, liver, adrenal and thyroid diseases.
- Pregnant or breast-feeding. Women who are pregnant or breast-feeding need additional water to stay hydrated and to replenish the fluids lost, especially when nursing. The Institute of Medicine recommends that pregnant women drink 2.3 liters (nearly 10 cups) of fluids a day and women who breast-feed consume 3.1 liters (about 13 cups) of fluids a day.
Beyond the tap: Many sources of water
You don’t need to sip from your water bottle all day to satisfy your fluid needs. Your diet, including the beverages you drink, can provide a large portion of what you need. In an average adult diet, food provides about 20 percent of total water intake. The remaining 80 percent comes from beverages of all kinds.
Fruits and vegetables – besides being good sources of vitamins, minerals and fiber – contain lots of water. For example, oranges are 87 percent water, and cucumbers are 95 percent water. Milk, juice and other beverages also have large amounts of water. Conversely, dried fruits, nuts, grain products and baked goods generally contain less water.
Make it count: Meet your water needs through food and beverages
Alcohol – such as beer and wine – and caffeinated beverages – such as coffee, tea or soda – can contribute to your total fluid intake. But your best beverage is still water. Water is calorie-free, inexpensive when drawn from a faucet or fountain, and readily available in and out of your home.
Thirst not always a reliable gauge
If you’re healthy and not in any dehydrating conditions, you can generally use your thirst as an indicator of when to drink water. But thirst isn’t always an adequate gauge of your body’s need for fluid replenishment. The older you are, the less you’re able to sense that you’re thirsty. And during vigorous exercise, an important amount of your fluid reserves may be lost before you feel thirsty. So make sure that you’re sufficiently hydrated before, during and after exercise.
Increased thirst and increased urination, both in volume and frequency, can be signs and symptoms of diabetes. With diabetes, excess blood sugar (glucose) in your body draws water from your tissues, making you feel dehydrated. To quench your thirst, you drink a lot of water and other beverages and that leads to more frequent urination. If you notice unexplained increases in your thirst and urination, see your doctor. It may not necessarily mean you have diabetes. It could be something else. And some people consume large amounts of water and experience increased urine output not associated with any underlying disease.
Diabetes – Staying safely hydrated
Make a conscious effort to keep yourself hydrated and make water your beverage of choice. Nearly every healthy adult can consider the following:
- Drink a glass of water with each meal and between each meal.
- Take water breaks instead of coffee or tea breaks.
- Substitute sparkling water for alcoholic drinks at social gatherings.
If you drink water from a bottle, thoroughly clean or replace the bottle often. Every time you drink, bacteria from your mouth contaminate water in the bottle. If you use a bottle repeatedly, make sure that the bottle is designed for reuse. To keep it clean, wash your container in hot, soapy water or run it through a dishwasher before refilling it.
Though uncommon, it’s possible to drink too much water. Drinking excessive amounts can overwhelm your kidneys’ ability to get rid of the water. This can lead to hyponatremia, a condition in which excess water intake dilutes the normal amount of sodium in the blood. People who are older, who have certain medical conditions such as congestive heart failure and cirrhosis, or who are taking certain diuretics are at higher risk of hyponatremia.