Do You Really Need To Drink Two Litres Of Water A Day? New Study Says No

It's a widely believed notion, often recommended by doctors and experts, that a person should drink at least two litres of water every day to stay healthy and hydrated. However, new research has found that the recommended eight glasses of water a day may be too much. Though it is not exactly harmful, it is also not needed in most circumstances. 

Scientists from the University of Aberdeen recently collaborated with other researchers to understand how much water people really need to be drinking. They looked at 5,604 people from across 23 different countries, aged between eight days and 96 years old, BBC reported. 

The findings of the survey which were published in Science, stated that people only require about 1.5 to 1.8 litres a day, lower than the two litres typically recommended.  

The research involved people drinking a glass of water in which some of the hydrogen molecules were replaced by a stable isotope of the element called deuterium, which is found naturally in the human body and is completely harmless. The rate of elimination of the extra deuterium shows how quickly the water in the body is turning over. People with a higher water turnover usually need to drink more water. 

The report suggests that people who live in hot and humid environments and at high altitudes, as well as athletes and pregnant and breastfeeding women, need more water as the water turnover is higher among them.  According to the research, men aged between 20-35 turned over an average of 4.2 litres per day, while women aged 20-40, turned over 3.3 litres. 

Prof John Speakman from the University of Aberdeen told BBC Radio's Good Morning Scotland that the original estimate of two litres a day comes from a slight miscalculation. "The water that we'd need to drink is the difference between the total water that we need to ingest and the amount that we get from our food. The way they estimated the amount of food was by asking people how much they eat. Because people under-report how much they eat, there's a misestimate and so you overestimate the amount of water that's needed,'' he noted. 

Mr Speakman also clarified that water turnover is not equal to the requirement for drinking water.  

He said, "Even if a male in his 20s has a water turnover of 4.2 litres per day, he does not need to drink 4.2 litres of water each day. About 15% of this value reflects surface water exchange and water produced from metabolism. The actual required water intake is about 3.6 litres per day. Since most foods also contain water, a substantial amount of water is provided just by eating.''