How Many Liters of Water Should You Drink per Day?

Water is the main chemical component of our body. The human being can survive much longer without consuming food than without drinking water. We need much water, that around 60% of our body weight is made just for her.


Dehydration, which is the name we give to the reduction of water volume in the body, can cause serious health problems, even death in severe cases. On the other hand, excessive consumption of water can also be detrimental as it can lead to a frame called water intoxication, which can be fatal in some circumstances.

So back to the question that gives title to this article, how many liters of water should you drink a day? The answer is: it depends. There is no magic number of liters that is suitable for the entire population. Several factors can cause an individual need more or less water than others. The famous rule that says we should drink 2 liters of water a day (or 6 to 8 glasses of water) is actually an empirical orientation, with little grounding in scientific evidence.

In this article we will explain what are the factors that one must take into account in deciding the amount of water that she should eat throughout the day. We will also explain what the water intoxication and how it arises.

As we said in the introduction, the amount of daily water each person needs to ingest is very individual. Some people need a lot, others need little. To facilitate the understanding of the subject, let's start talking about the article, in brief and simple, about how our body handles the volume of body water.

Water distribution in the body

If approximately 60% of our weight is water, this means that a person of 70 kg has about 42 kilograms or 42 liters of water in the body (1 liter of water weighs 1 kilogram). Of these 42 kg 2/3 (28 kilos or 28 liters) are within the cells and 1/3 (14 kg or 14 L) lies outside the cells. From 14 liters of water lying outside the cells, about 10 liters are distributed among tissues and organs (space which is called interstitial), and 4 liters are effectively only within blood vessels. Therefore, the entire body of water, only about 7% lies within the blood.

Dehydration is, therefore, a condition which affects many more cells and tissues that proper blood flow volume. When an individual loses 3 liters of body water, it loses two liters in the cells, 800 ml tissue and only 200 ml blood. Therefore, the patient begins to suffer the effects of dehydration of the cells long before presenting a significant drop in blood pressure, which only occurs in severe cases of dehydration.

Similarly, when the body meets with excess water, the distribution takes place similarly, with the intracellular and interstitial the most affected, which may cause swelling on cells and organs, including the brain.

How body controls the amount of water in the body?

The agency that controls the amount of water in the body is the kidney, and he does it very accurately. Small increases or decreases the amount of body water are sufficient to pass the kidneys to eliminate more or less water in the urine. In view of this, even if consummated water so short or longer than necessary, the kidneys will act to keep the volume of body water balanced, making you urinate more or less throughout the day.

Obviously, the correction ability of the kidneys has a limit. To eliminate toxins and substances filtered in the blood, the kidney must eliminate at least about 400-500 ml of water per day, otherwise would not dilute the chemicals. If the patient is very dehydrated, and the kidney is so eager to retain water in the body that it almost ceases to urinate, the individual goes into acute renal failure. And even when the patient to fully urinate, if the individual does not moisturize, water scarcity will continue worsening, as there is fluid losses by other means, such as sweat and feces, which can not be interrupted or adjusted (explain later).

Conversely, in excess of states of water body, the kidney is able to increase the production of urine up to 500 to 600 ml per hour, which gives about 12 liters of urine per day. If the patient consumes large amounts of water throughout the day to maintain a stable volume of body water, the kidney needs to produce large amounts of urine, causing the patient to feel comfortable going to the bathroom all the time. As the desire to urinate often arises when the volume of urine in the bladder is between 300 and 400 ml, just the kidney produce 300 ml of urine per hour so that the person needs to go to the bathroom in time to time.

Because the kidney can only produce a maximum of 600 ml urine per hour, where the individual for any reason decides to consume 5 liters of water at once, the excessive amount of water will be distributed in the cells, causing swelling the same in a potentially fatal complication called water intoxication. The kidneys will only be able to control the volume of body water after a few hours, which in some cases may be too late. At the end of this article we will explain this issue in more detail.

The amount of water that we consume daily should be that which is necessary for helping the kidneys to maintain stable body water volume. But why this value can vary so much from individual to another? For several reasons, for example:

a) basal amount of body water

Children have proportionally more water in the body than adults, which in turn are more water elderly. Men have more water than women. People obese, muscular or have very high amount of different body water of skinny or incredibly low personnel. Just so we set a magic number of daily water consumption to serve the entire population would be difficult. But there are other more relevant issues, as discussed below.

b) water losses throughout the day

Basically, our organism loses water in 4 different ways:

• Urine volume - about 1 to 2 liters per day.
• Sweat and evaporation of water from the skin - about 300-500 ml per day.
• Evaporation of water by respiration - about 200-400 ml per day
• Leaks in the stool - about 100 to 200 ml water per day.

This means that our body daily loses about 1.5 to 3 liters per day, good part of it is imperceptible, which is called insensible water loss. It is because these 1.5 and 3 liters of loss of basal water is very common to hear advice to consume around 1.5 to 3 liters of water per day.

However, the above values are only approximate, estimated in everyday situations. In many hot days, e.g., water loss through the skin is much greater than that in cold weather. We lost daily about 400 ml of water from the skin when the temperature is around 20°C, but this loss may be greater than 1 liter when the thermometer goes 35°C. Likewise, in one 20 minute session of sauna can lose up to 500 ml of water. Fever patients also lose more water from the skin more than usual.

The practice of physical activity also influences the water loss through the skin. Every hour of heavy exercise, the body can lose more than 1 liter of water, depending on the outside temperature. In a marathon, for example, you can lose more than 5 liters of water.

The loss of water by breathing also increase during the year, reaching 600 ml per day. People who live at sea level and rises to above 2500 meters end up losing more water into the respiratory tract altitudes because the reduced availability of oxygen causes them to increase lung work and accelerate the respiratory rate.

Another common situation that can dramatically change the amount of water lost is the occurrence of diarrhea or vomiting. A patient with food poisoning easily loses 1 liter of water daily by vomiting and / or diarrhea.

c) Amount of water in food

The water we consume comes not only of the net. All foods have water, in some greater or lesser amount. In general, only through feed could ingest approximately 0.5 to 1 liter of water per day. Soups, yogurts, ice cream, jelly and other foods that take the liquid form at room temperature should be recorded as net consumption. Among solid foods, fruits and vegetables are usually the most water-rich, like watermelon, oranges, tomatoes, lettuce, cucumbers, peppers, cauliflower, etc.

So as we can see, the water needs vary not only from individual to individual, but also from one day to the other. The famous recommendation of 2 liters of water a day may be enough for some cases, but it sure will be insufficient in many situations.

Our body is equipped with some defense mechanisms against dehydration. Every time the volume of body water is reduced and the cells begin to dehydrate the brain makes use of two actions: the emergence of the feeling of thirst and the release of hormones that stimulate the kidneys to retain water.

So if you have often thirsty and your urine is too concentrated, ie with little water, this is a sign that your body is trying to make a state of lack of water.

The thirst mechanism is very sensitive and is often activated in very early stages of dehydration. Our mouth and pharynx are rich in receptors that identify quickly the person is consuming water, why the sensation of thirst disappears so drink water. The brain knows you drank water before it was absorbed from the gastrointestinal tract and distributed by the body's cells. Cold water stimulates these receptors more strongly, so when we established, it appears to be more effective than water at ambient temperature, although hydrating the same.

The thirst mechanism is very important, but it may not be as reliable in some people, especially the elderly or sick individuals. A simple way to tell if the person is dehydrated even without thirst is to evaluate how wet are the tongue and inside the mouth. If during the day the individual has the mouth and tongue and dry, with no sign of saliva, it is a sure sign of dehydration.

The color of urine is another way to assess a person's hydration status. A very yellow urine with a strong odor indicates that the kidneys are retaining water. On the other hand, a completely transparent urine colored with water and in large volumes, that means the kidneys are excreting high amounts of water body. In general, healthy urine is one with a very light yellow.

A third way to assess the hydration status is by weight. Weigh yourself before and after doing some physical activity. The difference is the amount of water you lost during this period. You can do the same at work, weighing up right after breakfast and before lunch. If after breakfast you weighed 71 kilos before lunch and weighs 70.6 kg (without having eaten anything in that period), it means that you've lost about 400 grams (400 ml) of water will be shown. This serves as a basis for medium coarse calculate how much you lose water per hour at work.

Therefore, you should drink water when you are thirsty. If you thirst several times a day, that's a sign you need to increase water consumption. Increase water intake also if your urine is too concentrated persistent.

Water intoxication is a much more common than people realize event. The water becomes toxic when it is consumed in quantities much higher than necessary in a relatively short time, diluting the blood and causing the blood sodium concentration drops to dangerous levels acutely.

Water intoxication has been widely reported in participants in marathons, triathlons or other contests of intense effort. When sweat prolonged way, the body loses large amounts of water and mineral salts, particularly sodium (Na+), which is the main electrolyte blood. When this athlete is only re-hydrates with water, it resets the body needs water, but the amount of minerals lost in sweat, which leads to a lower frame sodium concentration in the blood, known as hyponatremia. If the athlete during the race consumes a water volume greater than the one he lost in sweat, the risk of hyponatremia becomes even higher.

The substitution of water for commercial isotonic not much change the situation because they have a low sodium concentration. A bottle Gatorade, for example, has a sodium concentration of only 23 meq / L, which is much below 140 meq / L of our blood. Therefore, despite being a little better than pure water, isotonic drinks, if consumed in large quantities, can also cause hyponatremia.

Currently, it is recommended that athletes consume water according to its headquarters. Thus, the body can more safely control the amount of water and sodium from the body.

Degrees of light hyponatremia usually do not cause symptoms, particularly if the reduction is sodium settling slowly over several days. However, cases of severe and acute hyponatremia, as are those that occur in cases of water intoxication can cause brain swelling and even death.

Water intoxication occurs not only in athletes who rehydrate incorrectly. In 2007, a fatal case of poisoning has become very famous in the US. During a contest sponsored by a radio, which rewarded the participant to drink more water and could hold the urine, a 28-year-old woman developed a serious frame of water intoxication and died at home hours after the contest.

Some people with mental problems usually drink water in an uncontrolled manner and may drink more than 10 to 15 liters per day, which is a risk factor for water intoxication occur.