How much water should you drink a day?
You need fluid every day. You do not need a magic number of glasses. Thirst, urine color, climate, and activity are better guides than a fixed rule. This page clears up the eight-glasses myth and offers simple cues.
Where the eight glasses idea came from
A round number is easy to remember. It is not a careful medical rule for every body. Needs vary with size, sweat, salt intake, and health. People with certain heart or kidney conditions may need fluid limits from a doctor. Most healthy adults can trust thirst and ordinary meals.
Simple cues that work
Thirst: drink when you are thirsty. Do not ignore it for hours on purpose.
Urine color: pale yellow or straw is a good everyday target. Dark yellow often means drink more. (Some vitamins turn urine bright yellow — that is different.)
Activity and heat: when you sweat, replace fluid during and after. Water is usually enough. Long hard efforts may need salt as well — ask a coach or doctor for sport-specific plans.
Meals: soup, fruit, vegetables, tea, and coffee contribute. You do not need to drink only plain water.
When to be careful
See a doctor for sudden swelling, very low urine output, confusion, or if you have been told to limit fluids. Babies, frail older adults, and people who cannot feel thirst well need closer attention from caregivers. Extreme over-drinking of plain water is rare but can dilute blood sodium — more is not always better.
For how water fits into food patterns, see Nutrition. For salt and body chemistry, see Chemistry.
This is general information. For your own health, talk to a doctor.