Expert reveals how much water we should really drink in a day — it's not what we've been told

A physiology expert says we may have been "oversold" the need to drink more water.

Professor Lewis Halsey at Roehampton University says that although dehydration is a real concern, bodies are actually capable of doing without water in the short- and medium-term and that it's not necessary to constantly sip water throughout the day. He says your body is good at letting you know when you are thirsty and need to take on water.

“It’s a tricky one,” Prof Halsey told The Guardian. “Obviously people can become dehydrated. We are set up to have quite a high water turnover rate: we sweat it out to keep cool, and we therefore need to recover those fluids. However, we can, at least in the short or even medium term, lose quite a lot of fluids and be fine.”

Prof Halsey said the amount of water each person needed depended on the person, with bigger and more active people needing more. Other people who might need more water than the average person include those with low body fat levels, those in less humid climates and those whose diets are made up of more calorie-dense foods which are typically lower in water content. Prof Halsey warned that older people also need to take care to drink more water because they have reduced sensitivity to thirst and might become dehydrated without knowing.

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But Prof Halsey's general advice is: “Drink when you’re thirsty.” He added that you should not feel like you have to sip water throughout the say, saying: “The body is absolutely fine at dealing with intermittent bursts of water ingestion,”

The NHS says that most people "should aim to drink enough during the day so their pee is a clear pale yellow colour". And the Eatwell Guide recommends that people should aim to drink 6 to 8 cups or glasses of fluid a day. But water, lower-fat milk and sugar-free drinks, including tea and coffee, all count as fluid. You may need to drink more fluids if you're:

• pregnant or breastfeeding

• in a hot environment

• physically active for long periods

• ill or recovering from illness