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Water: How much should you
drink every day?
By Mayo Clinic staff
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How much water should you drink each day? — a simple question with
no easy answer. Just as you are unique, so are your water needs. And
how much water you need depends on many factors, including your health
status, how active you are and where you live.
Though no single formula fits all people, several guidelines are
available to help you estimate how much to drink each day. Delve into
your daily fluid needs to learn how your body uses water and what
factors may increase — or decrease — your water requirements.
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 |
| Fatigue |
| Headache |
| Dry mouth |
| Little or no urination |
| Muscle weakness |
| Dizziness |
| Lightheadedness |
| How much water do you need? |
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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 |
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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 re-hydration 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 |
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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.
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 |
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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.
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.
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| 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.
Marathon runners and 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.
Drinking too much water is rare in healthy adults who consume an
average American diet. Check with your doctor or a registered
dietitian if you're concerned about drinking too much or too little
water. He or she can help you determine the amount that's best for
you. |
April 22, 2005
NU00283
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