You should aim for about
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How much water should you drink a day? Based on your weight, activity and climate.
The old "eight glasses a day" rule is a rough guide, not a scientific target. A more personalised estimate scales with body weight, activity and climate; a common starting point is around 30–35ml per kilogram of body weight, more if you are active or in the heat. The calculator above gives a figure for your weight and activity level, which is a better baseline than a fixed number for everyone.
Food and other drinks count. You do not have to drink your entire requirement as plain water. Fruit, vegetables, soups, tea and coffee all contribute to hydration, so the amount of water to actively drink is less than the total. Very intense exercise or hot weather increases losses through sweat and raises the amount needed.
Let thirst and urine guide you. For healthy adults, thirst is a reliable signal, and pale-straw-coloured urine is a good sign you are well hydrated; dark yellow suggests you need more. There is little benefit to forcing large amounts beyond that, and drinking to a fixed schedule is rarely necessary unless a doctor has advised it.