You may have heard that you should aim to drink eight 8-ounce glasses of water per day. How much you should actually drink is more individualized than you might think. The Institute of Medicine (IOM) currently recommends that men should drink at least 104 ounces of water per day, which is 13 cups. They say women should drink at least 72 ounces, which is 9 cups. Even still, the answer to exactly how much water you should drink isn’t so simple.
While the eight glasses rule is a good start, it isn’t based on solid, well-researched information. Your body weight is made up of 60 percent water. Every system in your body needs water to function. Your recommended intake is based on factors including your sex, age, activity level, and others, such as if you’re pregnant or breastfeeding.
The current IOM recommendation for people ages 19 and older is around 3.7 liters for men and 2.7 liters for women. This is your overall fluid intake per day, including anything you eat or drink containing water in it, like fruits or vegetables.
Of this total, men should drink around 13 cups from beverages. For women, it’s 9 cups.
Recommendations for kids have a lot to do with age. Girls and boys between ages 4 and 8 years should drink 40 ounces per day, or five cups. This amount increases to 56 to 64 ounces, or 7 to 8 cups, by ages 9 to 13 years. For ages 14 to 18, the recommended water intake is 64 to 88 ounces, or 8 to 11 cups.
Women of reproductive age
If you’re pregnant or breastfeeding, your recommendations change. Pregnant women of all ages should aim to get 80 ounces, or ten 8-ounce glasses of water each day. Breastfeeding women may need to up their total water intake to 104 ounces, or 13 cups.
|Demographic||Daily recommended amount of water (from drinks)|
|children 4–8 years old||5 cups, or 40 total ounces|
|children 9–13 years old||7–8 cups, or 56–64 total ounces|
|children 14–18 years old||8–11 cups, or 64–88 total ounces|
|men, 19 years and older||13 cups, or 104 total ounces|
|women, 19 years and older||9 cups, or 72 total ounces|
|pregnant women||10 cups, or 80 total ounces|
|breastfeeding women||13 cups, or 104 total ounces|
You may also need to drink more water if you live in a hot climate, exercise often, or have a fever, diarrhea, or vomiting.
- Add an additional 1.5 to 2.5 cups of water each day if you exercise. You may need to add even more if you work out for longer than an hour.
- You may need more water if you live in a hot climate.
- If you live at an elevation greater than 8,200 feet above sea level, you may also need to drink more.
- When you have a fever, vomiting, or diarrhea, your body loses more fluids than usual, so drink more water. Your doctor may even suggest adding drinks with electrolytes to keep your electrolyte balance more stable.
Why do you need water?
Water is important for most processes your body goes through in a day. When you drink water, you replenish your stores. Without enough water, your body and its organs can’t function properly.
Benefits of drinking water include:
- keeping your body temperature within a normal range
- lubricating and cushioning your joints
- protecting your spine and other tissues
- helping you eliminate waste through urine, sweat, and bowel movements
Drinking enough water can also help you look your best. For example, water keeps your skin looking healthy. Skin is your body’s largest organ. When you drink plenty of water, you keep it healthy and hydrated. And because water contains zero calories, water can be an excellent tool for managing your weight, as well.
There are risks of drinking too little or too much water.
Your body is constantly using and losing fluids through actions like sweating and urinating. Dehydration happens when your body loses more water or fluid than it takes in.
Symptoms of dehydration can range from being extremely thirsty to feeling fatigued. You may also notice you aren’t urinating as frequently or that your urine is dark. In children, dehydration may cause a dry mouth and tongue, lack of tears while crying, and fewer wet diapers than usual.
Dehydration may lead to:
- confusion or unclear thinking
- mood changes
- kidney stone formation
Mild dehydration may be treated by drinking more water and other fluids. If you have severe dehydration, you may need treatment at the hospital. Your doctor will likely give you intravenous (IV) fluids and salts until your symptoms go away.
Drinking too much water may be dangerous to your health as well. When you drink too much, the extra water can dilute the electrolytes in your blood. Your sodium levels decrease and can lead to what is called hyponatremia.
- nausea or vomiting
- muscle spasms, cramps, or weakness
Water intoxication hyponatremia is uncommon. People with a smaller build and children are at a higher risk of developing this condition. So are active people, like marathon runners, who drink large quantities of water in a short period of time. If you may be at risk due to drinking large quantities of water for exercise, consider drinking a sports drink that contains sodium and other electrolytes to help replenish the electrolytes you lose through sweating.
Staying hydrated goes beyond just the water you drink. Foods make up around 20 percent of your total fluid requirements each day. Along with drinking your 9 to 13 daily cups of water, try to eat lots of fruits and vegetables.
Some foods with high water content include:
- green peppers
Tips for drinking enough water
You may be able to meet your water intake goal by drinking when you are thirsty and with your meals. If you need some extra help consuming enough water, check out these tips for drinking more:
- Try carrying a water bottle with you wherever you go, including around the office, at the gym, and even on road trips.
- Focus on fluids. You don’t have to drink plain water to meet your hydration needs. Other good sources of fluid include milk, pure fruit juices, tea, and broth.
- Skip sugary drinks. While you can get fluid from soda, juice, and alcohol, these beverages have high calorie contents. It’s still smart to choose water whenever possible.
- Drink water while out to eat. Drink a glass of water instead of ordering another beverage. You can save some cash and lower the total calories of your meal, too.
- Add some flair to your water by squeezing in fresh lemon or lime juice.
- If you’re working out hard, consider drinking a sports drink that has electrolytes to help replace the ones you lose through sweating.
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How Much Water Should You Drink Per Day?
The body is about 60% water, give or take.
We’re constantly losing water from our bodies, primarily via urine and sweat.
There are many different opinions on how much water we should be drinking every day.
The health authorities commonly recommend eight 8-ounce glasses, which equals about 2 liters, or half a gallon.
This is called the 8×8 rule and is very easy to remember.
However, there are other health gurus who think we’re always on the brink of dehydration and that we need to sip on water constantly throughout the day… even when we’re not thirsty.
As with most things, this depends on the individual and there are many factors (both internal and external) that ultimately affect our need for water.
I’d like to take a look at some of the studies on water intake and how it affects the function of the body and brain, then explain how to easily match water intake to individual needs.
Can More Water Increase Energy Levels and Improve Brain Function?
Many people claim that if we don’t stay hydrated throughout the day, our energy levels and brain function can start to suffer.
There are actually plenty of studies to support this.
In one study in women, a fluid loss of 1.36% after exercise did impair both mood and concentration, while increasing the frequency of headaches.
There are other studies showing that mild dehydration (1-3% of body weight) caused by exercise or heat can negatively affect many other aspects of brain function.
However, keep in mind that just 1% of body weight is actually a fairly significant amount. This happens primarily when you’re sweating a lot, such as during exercise or high heat.
Mild dehydration can also negatively affect physical performance, leading to reduced endurance.
Does Drinking a Lot of Water Help You Lose Weight?
There are many claims about water intake having an effect on body weight… that more water can increase metabolism and reduce appetite.
According to two studies, drinking 500 ml (17 oz) of water can temporarily boost metabolism by 24-30% (8).
The top line below shows how 500 ml of water increased metabolism (EE – Energy Expenditure). You can see how the effect diminishes before the 90 minute mark:
The researchers estimate that drinking 2 liters (68 ounces) in one day can increase energy expenditure by about 96 calories per day.
It may be best to drink cold water for this purpose, because then the body will need to expend energy (calories) to heat the water to body temperature.
Drinking water about a half hour before meals can also reduce the amount of calories people end up consuming, especially in older individuals.
One study showed that dieters who drank 500 ml of water before meals lost 44% more weight over a period of 12 weeks, compared to those who didn’t.
Overall, it seems that drinking adequate water (especially before meals) may have a significant weight loss benefit, especially when combined with a healthy diet.
Does More Water Help Prevent Health Problems?
There are several health problems that may respond well to increased water intake:
- Constipation: Increasing water intake can help with constipation, which is a very common problem.
- Cancer: There are some studies showing that those who drink more water have a lower risk of bladder and colorectal cancer, although other studies find no effect.
- Kidney stones: Increased water intake appears to decrease the risk of kidney stones.
- Acne and skin hydration: There are a lot of anecdotal reports on the internet about water helping to hydrate the skin and reducing acne, but I didn’t find any studies to confirm or refute this.
Do Other Fluids Count Toward Your Total?
Plain water is not the only thing that contributes to fluid balance, other drinks and foods can also have a significant effect.
One myth is that caffeinated drinks (like coffee or tea) don’t count because caffeine is a diuretic.
However, the studies show that this isn’t true, because the diuretic effect of these beverages is very weak.
Most foods are also loaded with water. Meat, fish, eggs and especially water-rich fruits and vegetables all contain significant amounts of water.
If you drink coffee or tea and eat water-rich foods, then chances are that this alone is enough to maintain fluid balance, as long as you don’t sweat much.
Trust Your Thirst… It’s There For a Reason
Maintaining water balance is essential for our survival.
For this reason, evolution has provided us with intricate mechanisms for regulating when and how much we drink.
When our total water content goes below a certain level, thirst kicks in.
This is controlled by mechanisms similar to things like breathing… we don’t need to consciously think about it.
For the majority of people, there probably isn’t any need to worry about water intake at all… the thirst instinct is very reliable and has managed to keep us humans alive for a very long time.
There really is no actual science behind the 8×8 rule. It is completely arbitrary.
That being said, there are certain circumstances that may call for increased water intake… that is, more than simple thirst commands.
The most important one may be during times of increased sweating. This includes exercise, as well as hot weather (especially in a dry climate).
If you’re sweating a lot, make sure to replenish the lost fluid with water. Athletes doing very long, intense exercises may also need to replenish electrolytes along with water.
Water need is also increased during breastfeeding, as well as several disease states like vomiting and diarrhea.
Older people may need to consciously watch their water intake, because some studies show that the thirst mechanisms can start to malfunction in old age.
How Much Water Is Best?
At the end of the day, no one can tell you exactly how much water you need. As with most things, this depends on the individual.
Do some self experimentation… some people may function better with more water than usual, while for others it only causes the inconvenience of more frequent trips to the bathroom.
That being said, I am not sure if the small benefits of being “optimally” hydrated are even worth having to consciously think about it. Life is complicated enough as it is.
If you want to keep things simple (always a good idea), then these guidelines should apply to 90% of people:
- When thirsty, drink.
- When not thirsty anymore, stop.
- During high heat and exercise, drink enough to compensate for the lost fluids.
- That’s it.
Water: How much should you drink every day?
How much water should you drink each day? It's a simple question with no easy answer.
Studies have produced varying recommendations over the years. But your individual water needs depend on many factors, including your health, how active you are and where you live.
No single formula fits everyone. But knowing more about your body's need for fluids will help you estimate how much water to drink each day.
Health benefits of water
Water is your body's principal chemical component and makes up about 60 percent of your body weight. Your body depends on water to survive.
Every cell, tissue and organ in your body needs water to work properly. For example, water:
- Gets rid of wastes through urination, perspiration and bowel movements
- Keeps your temperature normal
- Lubricates and cushions joints
- Protects sensitive tissues
Lack of water can lead to dehydration — a condition that occurs when you don't have enough water in your body to carry out normal functions. Even mild dehydration can drain your energy and make you tired.
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 National Academies of Sciences, Engineering, and Medicine determined that an adequate daily fluid intake is:
About 15.5 cups (3.7 liters) of fluids for men
About 11.5 cups (2.7 liters) of fluids a day for women
These recommendations cover fluids from water, other beverages and food. About 20 percent of daily fluid intake usually comes from food and the rest from drinks.
What about the advice to drink 8 glasses a day?
You've probably heard the advice, "Drink eight 8-ounce glasses of water a day." That's easy to remember, and it's a reasonable goal.
Most healthy people can stay hydrated by drinking water and other fluids whenever they feel thirsty. For some people, fewer than eight glasses a day might be enough. But other people might need more.
Factors that influence water needs
You might need to modify your total fluid intake based on several factors:
- Exercise. If you do any activity that makes you sweat, you need to drink extra water to cover the fluid loss. It's important to drink water before, during and after a workout. If exercise is intense and lasts more than an hour, a sports drink can replace minerals in your blood (electrolytes) lost through sweat.
- Environment. Hot or humid weather can make you sweat and requires additional fluid intake. Dehydration also can occur at high altitudes.
- Overall health. Your body loses fluids when you have a fever, vomiting or diarrhea. Drink more water or follow a doctor's recommendation to drink oral rehydration solutions. Other conditions that might require increased fluid intake include bladder infections and urinary tract stones.
- Pregnancy or breast-feeding. Women who are pregnant or breast-feeding need additional fluids to stay hydrated. The Office on Women's Health recommends that pregnant women drink about 10 cups (2.4 liters) of fluids daily and women who breast-feed consume about 13 cups (3.1 liters) of fluids a day.
Beyond the tap: Other sources of water
You don't need to rely only on what you drink to meet your fluid needs. What you eat also provides a significant portion. For example, many fruits and vegetables, such as watermelon and spinach, are almost 100 percent water by weight.
In addition, beverages such as milk, juice and herbal teas are composed mostly of water. Even caffeinated drinks — such as coffee and soda — can contribute to your daily water intake. But water is your best bet because it's calorie-free, inexpensive and readily available.
Sports drinks should be used only when you're exercising intensely for more than an hour. These drinks help replace electrolytes lost through perspiration and sugar needed for energy during longer bouts of exercise.
Energy drinks are different from sports drinks. Energy drinks generally aren't formulated to replace electrolytes. Energy drinks also usually contain large amounts of caffeine or other stimulants, sugar, and other additives.
Staying safely hydrated
Your fluid intake is probably adequate if:
- You rarely feel thirsty
- Your urine is colorless or light yellow
A doctor or registered dietitian can help you determine the amount of water that's right for you every day.
To prevent 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.
- Drink water if you're feeling hungry. Thirst is often confused with hunger.
Although uncommon, it's possible to drink too much water. When your kidneys can't excrete the excess water, the sodium content of your blood is diluted (hyponatremia) — which can be life-threatening.
Athletes — especially if they participate in long or intense workouts or endurance events — are at higher risk of hyponatremia. In general, though, drinking too much water is rare in healthy adults who eat an average American diet.