Water and the myth of eight glasses a day to dispel


A new study of thousands of people shatters the oft-repeated idea that eight glasses meet the human body’s daily requirement for good.


“Science has never backed up the old eight-cup idea as an appropriate guideline,” says Dale Schoeller, a professor emeritus of nutritional sciences at the University of Wisconsin-Madison who has been studying water and metabolism for decades. The total volume of body water is strictly controlled by sensitive mechanisms that also respond to internal variations in the organism. Estimates of daily water requirements are based on several factors: water is needed to replace losses which normally consist of losses (from the skin and respiratory tract), urine, perspiration. One of the mechanisms that help maintain fluid balance is fluid turnover .

The misunderstanding has arisen over the years because – evidently – the exchange (or turnover) made by the water in drinks overlapped with that which comes from the food you eat or from the type of life you lead.  Schoeller and his team publish a new study in which they bring enough evidence to support this thesis.

The study measured the water consumption of more than 5,600 people in 26 countries, aged 8 days to 96 years, and found average daily water consumption ranging from 1 liter per day to 6 liters per day. “There are also abnormal people who consume up to 10 liters a day,” says Schoeller.


Lifestyle and water intake

Previous studies on the topic relied largely on volunteers who either self-reported their water and food consumption, or were observations of dubious value as not representative of most people ‘s lifestyles . Therefore, in Scholler’s study, data from the participants were collected, comparing environmental factors – such as temperature, humidity and altitude of the cities of origin – with measurements of water exchange, energy expenditure, body mass , gender, age and physical condition. The researchers also incorporated the  Human Development Index (CSI) into their analyses of the United Nations, a composite measure of a country that combines life expectancy, school enrollment and economic factors.


The study shows that, other things being equal, men and women differ by about half a liter of water exchange. “People living in countries with low SSI are more likely to live in areas with higher average temperatures, do physical work and spend less time inside climate-controlled buildings during the day. This, in addition to the lower probability of having access to a sip of clean water every time they need it, means that their water turnover is higher”. says the professor.

Furthermore, according to Schoeller, these types of measurements will improve our ability to more specifically and accurately predict future water needs, especially in difficult circumstances.

  • Variation in human water turnover associated with environmental and lifestyle factors. (


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