Hydration advice ranges from sensible to bizarre. Here's what's actually supported.
How much?
The NHS suggests 6–8 cups or glasses of fluid a day for most adults. You'll need more in hot weather, when exercising, or if you're unwell.
Myth: only water counts
Water, milk, tea, coffee, sugar-free drinks and even the water in food (around a fifth of intake) all contribute. Moderate caffeine has only a mild diuretic effect.
Myth: if you're thirsty, you're already dehydrated
For healthy adults, thirst is a reliable signal. Drinking to thirst works well for everyday life.
Fact: urine colour is a useful guide
Pale straw-coloured urine generally indicates good hydration. Dark yellow suggests you should drink more.
Fact: you can drink too much
Drinking very large volumes during long endurance events can dilute blood sodium (hyponatraemia), which can be dangerous. Drink to thirst and include sodium during long, sweaty sessions.
Who needs extra care?
Older adults, who may feel less thirsty; young children; people with diarrhoea or vomiting; and anyone exercising hard in the heat.