How much water should we drink every day? Most health advice, including from the NHS, typically recommends drinking between six to eight glasses of fluid, including water, a day – equivalent to between 1.2 to two litres.
However, this advice has come under scrutiny in recent years. Some claim that drinking lots of water can flush out toxins and maintain healthy kidneys, but some studies have shown that drinking more water does not offer more benefits.
Now, a new study suggests that drinking two litres of water per day is likely too much for most people in most situations.
Scientists from the University of Roehampton London (UoRL) conducted “the biggest study of its kind” with more than 5,600 participants between the ages of eight and 96 from 23 different countries.
They found that a “one size fits all” policy for water intake does not work for everyone depending on a number of factors, including age, sex, location, occupation, and more.
The recommended amount of daily water intake, which is also promoted by the European Food Safety Authority, is “not supported by the research data”, the study authors said.
The research comes after a separate study suggested that film star Bruce Lee’s death in 1973 may have been caused by drinking too much liquid.
In a paper published in the Clinical Kidney Journal, scientists proposed that the renowned martial artist’s kidneys were unable to excrete excess water, which led to cerebral oedema (swelling of the brain).
They pointed to factors that suggested Lee may have been consuming unusually high quantities of liquid at the time due to his diet.
The authors wrote: “We hypothesise that Bruce Lee died from a specific form of kidney dysfunction: the inability to excrete enough water to maintain water homeostasis.”
Researchers from UoRL found that “water turnover”, which refers to total intake and water loss movement of the body, is higher in hot and humid environments and at high altitudes.
It is also higher among athletes, pregnant and breastfeeding women, and individuals who undertake high levels of physical activity.
Males between the ages of 20 and 35 had the highest levels of energy expenditure, which meant their water turnover was higher. The study recorded an average of 4.2 litres per day in this group. However, the water turnover decreases as they get older, averaging only 2.5 litres per day in males in their nineties.
Among women, the average water turnover between the ages of 20 to 40 was 3.3 litres per day, which dropped to around 2.5 litres per day by the age of 90.
The study also sheds light on the role of food when it comes to water intake. Food accounts of more than half of the standard amount of water intake per day.
In fact, it found that the average male from US or Europe should only be drinking between 1.5 to 1.8 litres of water per day after water intake from food is taken into account, while women should only have 1.3 to 1.4 litres.
But it also depends on other factors. Older people will generally require less water, but living in a hot climate or being pregnant or breast-feeding will require an increase in this water demand.
The study authors say that the outcomes of the paper, published in the journal Science, can be used to “anticipate the effects of future changes such as climate and population demography”, as well as helping countries “anticipate their future water needs”.
Professor Lewis Halsey from the UoRL said: “Water is essential for human survival and measuring our exact water requirements continues to remain a challenge.
“This research sheds light as to how factors including climate, age, physical activity, pregnancy and water intake of food can determine how much water intake we actually need.
“It is an important finding that can help create global public health policies regarding the provision of drinking water and water-rich food as concerns surrounding climate change, clean drinking water and global water security continue to grow around the world.”
