There are many health benefits to staying hydrated. From helping you manage your weight, to improving brain function, to reducing your risk of heart attacks, drinking enough water can keep your body functioning optimally. But how much water should you drink?
Scientists, doctors, and nutritionists have tried to come up with a definitive answer to this question, but the truth is, there isn’t one. How much water you should drink depends on a variety of factors, including age, size, and physical activity level.
That being said, there are ways to figure out how much water you need. It’s not an exact science, but understanding the factors that affect hydration and applying them to your own life will help you stay adequately hydrated.
How Much Water Should You Drink?
You have likely heard of the eight by eight rule. That rule suggests that healthy adults should drink eight glasses of water that are eight ounces each every day. Over the last twenty years, however, many experts have contested this rule, and it has essentially been debunked.
Many studies actually suggest that this amount of water may be too much for many people. In fact, a 2002 review of studies found that there is very little scientific evidence to back it up .
Many experts argue that the problem with this rule is that it ignores other sources of water. Many fruits and vegetables also provide H2O, which contributes to your hydration status. This means, then, that not all of your fluids need to come from pure water alone.
In 2004, the National Academy of Sciences released a report that set general guidelines for water consumption. These guidelines were based on national data, which found that women who seem to have a good hydration status drink on average 2.7 litres of water per day. Adequately hydrated men drink on average 3.7 litres.
This amount of water, however, did not come from pure H2O alone. This was the total water they consumed from all sources, including water, other beverages, and food.
Lawrence Appel is the chair of the panel that wrote the report and professor of medicine, epidemiology, and international health, Johns Hopkins University, Baltimore. He said that they don’t offer a rule of thumb for the number of glasses of water people should drink, because your hydration needs can be met through a variety of sources.
“While drinking water is a frequent choice for hydration, people also get water from juice, milk, coffee, tea, soda, fruits, vegetables, and other foods and beverages as well,” he explained .
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So how much water should you drink? The answer lies in something called fluid balance. Fluid balance is how your body ensures that the amount of water leaving it is equal to the amount that your body is taking in. The equation is very simple, and looks like this:
Fluid balance = amount of fluids in – the amount of fluids out 
Essentially, the amount of water you take in should equal the amount of water you excrete. If this gets out of balance, whether you’re dehydrated or overhydrated, it could cause the concentration of electrolytes in your body to be too high or too low. This can lead to health problems .
You lose water through normal physiological activities, like breathing, sweating, and urination. You replace that with food, drinking fluids, and through “aerobic respiration”. This is the process by which organisms turn food into fuel. A byproduct of this process is water. This amount, however, is small (roughly a cup per day) .
Factors that Influence How Much Water You Should Drink
There are many factors that influence how much water you need to drink in a day. Understanding how these factors affect you personally will help you determine how much water you need to stay hydrated.
Ages and Sex
On average, male bodies tend to contain more water than women’s. The bodies of younger people also tend to contain more water. For example, an infant who is less than six months old has an average body water content of about 74 percent. A man over fifty has an average body water content of about 56 percent, and a woman 47 percent .
For this reason, as you age you need to adjust your water intake to ensure you’re adequately hydrated.
Research from the University of Michigan found that adults with a higher BMI are more likely to experience dehydration. While there may be many reasons for this, the study suggests that people with larger bodies may need to consume more water in order to stay hydrated .
If you live somewhere where it is hot and dry, you will need to drink more water. Conversely, if you live near a large body of water where the humidity is higher, you may not need to drink as much .
If you exercise frequently and thus sweat more, you will need to drink more water to stay hydrated. In addition, muscle tissue contains more water than fat tissue. Since people who exercise regularly likely have more muscle tissue, this will also affect how much fluid they need to be taking in .
Women who are pregnant need to increase their water intake. Since pregnant women should also be eating more calories, some of this fluid can come from food. Still, doctors often encourage pregnant women to increase their water and other fluid intakes .
When you are ill, you are likely to lose more water than usual through sweating, vomiting, and diarrhea. For this reason, when you are sick you should focus on drinking enough fluids to stay hydrated. Doctors may recommend a beverage that contains electrolytes to keep your electrolytes from getting out of balance. Other conditions like diabetes may also affect your fluid balance because high blood sugar causes you to urinate more frequently .
How to Know How Much Water You Should Drink
Many experts have attempted to come up with a calculation to determine individual water needs, but the truth is that there isn’t one magic formula. The experts at the National Academy of Sciences, however, suggest that you let your body’s natural queue be your guide: thirst.
“We concluded that on a daily basis, people get adequate amounts of water from normal drinking behavior — consumption of beverages at meals and in other social situations — and by letting their thirst guide them,” they said .
When your hydration levels begin to drop, your body naturally feels thirsty to prompt you to drink.
The other reliable way to know if you’re drinking enough water is by looking at your urine. When you’re adequately hydrated, your pee should be pale yellow or clear. Dark yellow or orange, on the other hand, usually indicates dehydration .
Some health conditions, however, can make thirst or pee color an unreliable method for determining hydration status. If you are suffering from a health condition that may affect your hydration status, talk to your doctor about strategies for staying hydrated.
Other Sources of Water
Drinking pure water is not the only way to reach your hydration goal. While water is an excellent calorie-free hydrator, the following also count toward your total daily water intake:
- Food. Fruits and vegetables in particular contain large quantities of water that can keep you hydrated.
- Coffee or tea. There is a myth that caffeinated beverages actually cause your body to lose water because they’re diuretics. Studies show that they can cause excess urination in some, however for most they can help to add water to your body overall .
- Other drinks like juice, sports drinks, and sodas also contribute to your water intake. That being said, you should minimize the number of beverages you are consuming with added sugar. Those drinks may add water, but they can also lead to other health issues in excess.
How Much Water Should You Drink: The Bottom Line
There is no magic calculation that you can use to determine how much water you need to stay hydrated. If you’re a healthy adult, the best way to ensure you’re adequately hydrated is by listening to your body’s thirst mechanism. While there are factors that will influence how much water you need to drink, your body will adjust and let you know when you need fluids. If you’re an athlete for very active, preventative hydration is sometimes warranted, but it is also possible to overhydrate.
A healthy diet that includes lots of high-water-containing foods like fruits and vegetables will also help you to maintain proper hydration status. Beverages other than pure water can also contribute to your total fluid intake, although you should avoid consuming too many high-sugar beverages.
Chronic dehydration can affect your energy levels, brain function, and health status. If you listen to your body and give it what it needs, however, you can easily stay hydrated and avoid the problems caused by dehydration.
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