How much water do I need each day, and are eight glasses right for everyone?
There is no single water target for everyone. Heat, activity, body size, pregnancy and illness affect needs, and food and other drinks contribute to total intake. People prescribed fluid restriction should follow their clinical plan rather than a general target.
Details
What counts toward intake?
Plain water is a practical choice, but soup, milk, suitable drinks and moisture in food also contribute. References for total water therefore differ from recommendations expressed only as glasses of drinks.
Monitor hydration sensibly
Drink regularly and adjust appropriately for heat or sweating. Thirst and pale urine can offer clues, but neither is a precise test for everyone. Medicines, foods and illnesses may affect urine colour or thirst.
When fluids are part of treatment
Some kidney or heart conditions require a controlled fluid intake. Do not increase fluids to reach a popular target or restrict them without advice. Request a clear plan explaining the amount, what counts toward it, and what to do during vomiting, diarrhoea or changes in weight and swelling.
Related reading: Does coffee cause dehydration, and how much caffeine is too much?.