A recommendation to drink eight glasses of water a day is likely to be excessive for most people.

The suggestion has become accepted wisdom. People have a wide range of water intakes according to the most rigorous study to date on water turnover. The research shows that many people only need 1.5 to 1.8 litres a day.

One of the paper's first authors said that the current recommendation is not supported by science. The scientists don't know where the recommendation came from.

Estimates of water requirements have tended to ignore the water content of food, which can contribute a significant portion of our overall intake.

If you only eat bread and bacon and eggs you won't get much water from food, but if you eat meat, vegetables, fish, pasta and rice you can get about 50% of your water needs from food.

The study assessed the water intake of 5,604 people from 23 countries. The research involved people drinking a glass of water and replacing some of the hydrogen molecule with a stable isotope of the element deuterium, which is found naturally in the human body.

The rate of elimination of the extra deuterium shows how quickly water in the body is turned over, and the study found that the measure varied depending on a person's age, gender, activity levels and surrounding area. Athletes and pregnant and breastfeeding women need to drink more water because they have higher turnover.

Men aged 20 to 35 have the highest energy expenditure values, with an average of 4.2 litres a day. The average was 2.5 litres a day for men in their 90's. By the age of 90, women in the 20 to 40 age group had an average turnover of 2.5 liters. Non-athletes turn over less than athletes. Newborn babies replaced about 28% of the water in their bodies on a daily basis.

According to the study, the idea that we should all be drinking eight glasses of water is probably too high for most people in most situations.

He thinks it's a recommendation that many people ignore and follow what their body tells them.

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The authors point out that clean drinking water is not free to produce and that drinking more water than you need is unlikely to be harmful for health. Speakman said there was a cost to drinking more than we needed.

20 million litres of water is wasted every day if 40 million people in the UK follow the guidelines and drink half a liter of water more than they need.