How much water should we drink per day, including children?

How much water should we drink per day, including children?

by | Mar 2, 2023

Not long ago, I thought I was not drinking enough water per day. At home, I remember very well my mother’s two-liter water bottle on the kitchen counter, which she refilled every day with the intention of drinking it, even if she was not thirsty at all. She adhered to the rule that was “fashionable” in her time, that one must drink eight glasses of water a day. Surely she heard about its benefits on one of those morning “health and wellness” TV shows she used to watch.

My mother is not an exception. Many people believe you need to drink at least eight glasses of water per day to be healthy. Perhaps you are one of those (I was too!) or have friends and family who believe it. As a teacher, I frequently receive comments from concerned parents who believe their children are not drinking enough water.

A few years ago, I started to follow the work of a renowned Spanish nutritionist, Julio Basulto, and came across this article: “Beber en función de la sed, incluso en verano” [Drinking based on thirst, even in summer]:

[It is possible that the title that I have given this text sounds like “nutritional blasphemy”, since there are many messages around us inviting us to drink even if we are not thirsty, but I can assure you that the title is true. As the summer heat is approaching, and such messages are very likely to multiply, I think it is important to insist that, with a few exceptions, the thirst mechanism works well enough that we do not have to worry about living glued to a bottle of water]

So, how much water do we need, including children?

It seems there is no formal recommendation regarding the amount, as it varies depending on the person, the characteristics of the diet and the type of activity carried out. The answer according to different experts is, “it depends”. Here is a summary of what I have found during my research about this and other questions:

“Fluid needs vary quite a bit from person to person, and the old standby recommendation of eight to 10 cups a day has caught on with most people, though it’s not based on any science”.

“Most people can get the water they need from their usual diet and by drinking when they are thirsty.Especially in hot weather, we are urged to drink adequate fluids and be on guard for dehydration. That may be why you see people toting bottled water everywhere, propelled by the myth that you need to drink eight glasses of water a day to be healthy. […] you may not need to drink that much water every day to prevent dehydration”.

Abel Mariné, Emeritus Professor of Nutrition and Bromatology at the University of Barcelona, points out that although it is recommended to drink two liters of water a day, this does not mean that you must live attached to a glass, since food also provides water: the content of Water varies between 85 and 95% in fresh vegetables (such as tomatoes), 80-86% of fruits, 80% of lean fish or 75% of eggs. There is also water in coffee, milk, horchata and gazpacho, for example. Or a cooked rice can contain between 70-80% water (pasta has 60-70%), so if a person has a healthy diet (that is, rich in vegetables and fruits and poor in processed products), more than a liter of water is provided by the food you eat.

“Drink at least eight glasses of water a day!” Not necessarily, says a DMS physician Heinz Valtin, MD. The universal advice that has made guzzling water a national pastime is more urban myth than medical dogma and appears to lack scientific proof, he found.

Valtin, a kidney specialist and author of two widely used textbooks on the kidney and water balance, sought to find the origin of this dictum and to examine the scientific evidence, if any, that might support it. He observed that we see the exhortation everywhere: from health writers, nutritionists, even physicians. Valtin doubts its validity. Indeed, he finds it, “difficult to believe that evolution left us with a chronic water deficit that needs to be compensated by forcing a high fluid intake.”

Is yellow urine synonym of dehydration?

To my surprise, “It is important to address the potential bias of first morning urine samples. Even in well-hydrated children, the effect of antidiuretic hormone at night produces highly concentrated urine in the first morning specimen”.

Should we then trust our body’s thirst mechanism?

Thirst is the body’s mechanism to increase water consumption in response to detected deficits in body fluid or, differently said, is the message our body send us that we need to reach for a glass of water.

“Thirst has long been thought of as a negative homeostatic feedback response to increases in blood solute concentration or decreases in blood volume. However, emerging evidence suggests a clear role for thirst as a feedforward adaptive anticipatory response that precedes physiological challenges”.

“Thirst is an adequate stimulus to prevent intracellular and extracellular dehydration”.

Potential risks?

Let’s listen to experts:

“The proposed health benefits of drinking fluids beyond regulatory need is unsubstantiated by scientific evidence, including a panel of experts assembled by the Institute of Medicine. And although the recommendation to drink more water seems harmless enough, the threat of drinking beyond thirst carries the risk of serious medical consequences from low blood [Na+] (dilutional hyponatremia), especially during exercise, and has resulted in the deaths of two high school athletes in the past year. Thus, we urge public health professionals to critically examine the physiological evidence underlying the use of a Uosm threshold of 800 milliosmoles per kilogram of water for “dehydration” before enacting policies encouraging children to drink beyond their thirst. The potential dangers may outweigh any perceived cognitive or health benefit, with the approximately 33% intake of sugar-sweetened beverages perhaps the more serious detriment to health”:

Could insufficient water intake cause constipation?

There also does not appear to be convincing evidence that constipation is from lack of hydration. Studies point out to clear relationship between low dietary fiber intake and constipation. “Increase of dietary fiber intake has been recommended to treat constipation in children and adults”.


It seems we have become used to hearing and even happily using terms like “dehydration”, “detox”, “inflammation”. But have we stopped to really think what these words mean? I agree with nutritionists, such as Julio Basulto, among others, who invite us to mistrust those so-called nutrition advice, usually disguised with a “sciencey” terminology, based more on beliefs than on tested evidence, and often used by the food industry with the aim of trying to sneak in a product to sell.

As Marion Nestle, American professor of nutrition, food studies and public health, explains:

“I am not against encouraging kids to drink water.


  • “Water deficiency is not a public health problem in the United States. Childhood obesity is the problem.
  • Drinking water will only help to counter childhood obesity if it substitutes for sugary sodas.
  • Bottled water companies such as Dasani (owned by Coca-Cola) and Aquafina (PepsiCo), and their trade group The American Beverage Association (ABA), are the main supporters of this initiative [referring to Michele Obama’s “Drink Up: You Are What You Drink” campaign]
  • This makes the message sounds like “drink bottled water,” without much attention to environmental implications”.
Following the principles of the Positive Discipline, and what it has been said above, as a teacher my recommendation to parents and educators would be, rather than focusing on how much water we should drink, let's focus on:
The parent’s role: Provide water and healthy meals
· Determine beverages to offer to your child 
· Choose water instead of sodas or other sugary drinks
· Model good eating and drinking habits 
· Model environmentally friendly habits: avoid bottled water as much as possible
The children’s role: to make their own choices
· To choose how much water they will drink
· To decide if they are thirsty at all


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