Water is essential to good health, yet needs vary by individual. These guidelines can help ensure you drink enough fluids.By Mayo Clinic Staff
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.
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:
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.
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:
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.
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.
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.
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 (1).
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.
According to two studies, drinking 500 ml (17 oz) of water can temporarily boost metabolism by 24-30% (8).
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.
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 (12).
Overall, it seems that drinking adequate water (especially before meals) may have a significant weight loss benefit, especially when combined with a healthy diet.
There are several health problems that may respond well to increased water intake:
Plain water is not the only thing that contributes to fluid balance, other drinks and foods can also have a significant effect.
However, the studies show that this isn’t true, because the diuretic effect of these beverages is very weak (22).
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.
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 (23).
There really is no actual science behind the 8×8 rule. It is completely arbitrary (24).
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.
people may need to consciously watch their water intake, because some
studies show that the thirst mechanisms can start to malfunction in old
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: