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The ultimate guide to hydration and what you really should be drinking

Plain water, coffee or milk? Sports or energy drinks? Our ideas about what we ought to be drinking, and how much, are confounded by half-truths. Here's what the science says

By David Cox

5 September 2023


Bill Diodato

RECENTLY, I have become somewhat obsessed with a new index on my smartwatch that purports to calculate whether I am sufficiently hydrated. The idea is to prompt the wearer to drink enough fluids to avoid dehydration. A watch tracking hydration might sound like a gimmick, but new research suggests there could be lasting health effects to being even mildly dehydrated.

One stumbling block I have faced on my hydration mission is that I find plain water, well, plain boring. But these days, there are myriad other types of fluid available, from sports and energy drinks to coconut water. Then there’s my personal favourite: coffee. Aside from taste, are any of these a suitable substitute, in terms of both my health and hydration? Do I even need to think this much about my fluid intake?

Our notions about what we ought to be drinking are confounded by half-truths and questionable health claims. So, here is a guide to modern hydration, cutting through the hype to discover the science about what we really should be drinking – and how much.

Water is the main constituent of the human body, making up around half of our adult body mass. The body’s balance of water intake and output is tightly regulated to keep the concentration of salts and minerals, or electrolytes, in our blood at a precise level. To prevent dehydration, hormonal and neural mechanisms are activated, stimulating thirst to encourage water intake and increased water reabsorption by the kidneys to decrease water output.

How much water should you drink?

The question of whether we are drinking enough for optimal health has been a matter …

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