Water: How much should you drink every day?
Water is
essential to good health, yet needs vary by individual. These guidelines can
help ensure you drink enough fluids.
Although
no single formula fits everyone, knowing more about your body's need for fluids
will help you estimate how much water to drink each day.
How much water do you need?
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 Institute of Medicine determined that an adequate intake (AI) for
men is roughly 3 liters (about 13 cups) of total beverages a day. The
AI for
women is 2.2 liters (about 9 cups) of total beverages a day.
What about the advice to drink eight glasses a day?
Everyone
has heard the advice, "Drink eight 8-ounce glasses of water a day."
That's about 1.9 liters, which isn't that different from the Institute of
Medicine recommendations. Although the "8 by 8" (8 glass of water in
8 hours) rule isn't supported by hard evidence, it remains popular because it's
easy to remember. Just keep in mind that the rule should be reframed as:
"Drink at least eight 2 liters glasses of fluid a day," because all
fluids count toward the daily total.
Factors that influence water needs
You may
need to modify your total fluid intake depending on how active you are, the
climate you live in, 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 need to drink extra water to
compensate for the fluid loss. An extra 400 to 600 milliliters (about 1.5
to 2.5 cups) of water should suffice for short bouts of exercise, but
intense exercise lasting more than an hour (for example, running a
marathon) requires more fluid intake. How much additional fluid you need
depends on how much you sweat during exercise, and the duration and type
of exercise. During long bouts of intense exercise, it's best to use a
sports drink that contains sodium, as this will help replace sodium lost
in sweat and reduce the chances of developing hyponatremia, which can be life-threatening.
Also, continue to replace fluids after you're finished exercising.
- Environment. Hot or humid weather can
make you sweat and requires additional intake of fluid. Heated indoor air
also can cause your skin to lose moisture during wintertime. Further,
altitudes greater than 8,200 feet (2,500 meters) may trigger increased
urination and more rapid breathing, which use up more of your fluid
reserves.
- Illnesses or health
conditions.
When you have fever, vomiting or diarrhea, your body loses additional
fluids. In these cases, you should drink more water. In some cases, your
doctor may recommend oral rehydration solutions, such as Gatorade,
Powerade or CeraLyte. Also, you may need increased fluid intake if you
develop certain conditions, including bladder infections or urinary tract
stones. On the other hand, some conditions such as heart failure and some
types of kidney, liver and adrenal diseases may impair excretion of water
and even require that you limit your fluid intake.
- Pregnancy or breast-feeding. Women who are expecting or
breast-feeding need additional fluids to stay hydrated. Large amounts of
fluid are used especially when nursing. The Institute of Medicine
recommends that pregnant women drink 2.3 liters (about 10 cups) of fluids
daily and women who breast-feed consume 3.1 liters (about 13 cups) of
fluids a day.
Beyond the tap: Other sources of water
Although
it's a great idea to keep water within reach at all times, you don't need to
rely only on what you drink to meet your fluid needs. What you eat also
provides a significant portion of your fluid needs. On average, food provides
about 20 percent of total water intake. For example, many fruits and
vegetables, such as watermelon and tomatoes, are 90 percent or more water by
weight.
In addition,
beverages such as milk and juice are composed mostly of water. Even beer, wine
and caffeinated beverages — such as coffee, tea or soda — can contribute, but
these should not be a major portion of your daily total fluid intake. Water is
still your best bet because it's calorie-free, inexpensive and readily
available.
Staying safely hydrated
Generally
if you drink enough fluid so that you rarely feel thirsty and produce 1.5
liters (6.3 cups) or more of colorless or light yellow urine a day, your fluid
intake is probably adequate. If you're concerned about your fluid intake or
have health issues, check with your doctor or a registered dietitian. He or she
can help you determine the amount of water that's right for you.
To ward
off dehydration and make sure your body has the fluids it needs, make water
your beverage of choice. It's also a good idea to:
- Drink a glass of water or
other calorie-free or low-calorie beverage with each meal and between each
meal.
- Drink water before, during
and after exercise.
Although
uncommon, it is possible to drink too much water. When your kidneys are unable
to excrete the excess water, the electrolyte (mineral) content of the blood is
diluted, resulting in low sodium levels in the blood, a condition called
hyponatremia. Endurance athletes, such as marathon runners, who drink large
amounts of water, are at higher risk of hyponatremia.