How much water should you drink a day?

In the early 19th Century, people had to be close to death before deigning to drink water. Only those “reduced to the last stage of poverty satisfy their thirst with water”, according to Vincent Priessnitz, the founder of hydropathy, otherwise known as “the water cure”.

Many people, he added, had never drunk more than half a pint of plain water in one sitting.

How times have changed. Adults in the UK today are consuming more water now than in recent years, while in the US, sales of bottled water recently surpassed sales of soda. We’ve been bombarded with messages telling us that drinking litres of water every day is the secret to good health, more energy and great skin, and that it will make us lose weight and avoid cancer.

Commuters are encouraged to take bottles of water onto the London Underground, pupils are advised to bring water into their lessons and few office meetings can commence without a giant jug of water sitting in the middle of the desk.

Fuelling this appetite for water is the “8x8 rule”: the unofficial advice recommending we drink eight 240ml glasses of water per day, totalling just under two litres, on top of any other drinks.

That “rule”, however, isn’t backed by scientific findings – nor do UK or EU official guidelines say we should be drinking this much.

Where did it come from? Most likely, it seems, from misinterpretations of two pieces of guidance – both from decades ago.

In 1945 the US Food and Nutrition Board of the National Research Council advised adults to consume one millilitre of liquid for every recommended calorie of food, which equates to two litres for women on a 2,000-calorie diet and two-and-a-half for men eating 2,500 calories. Not just water, that included most types of drinks – as well as fruits and vegetables, which can contain up to 98% water.