Eight glasses a day. Two litres. Three litres.
There is no shortage of advice about how much water we should drink. But there is no single amount that is right for everyone.
Our water needs change from person to person — and even from day to day.
The better question is not simply “How many glasses should I drink?” but “Am I replacing the water my body actually needs?”
What Do Official Recommendations Say?
The European Food Safety Authority gives general reference values for total daily water intake of approximately:
* 2.0 litres for women * 2.5 litres for men
But there is an important detail that is often missed.
These figures include all water consumed during the day — not just glasses of plain water.
Water also comes from tea, coffee, milk and other drinks, as well as foods. Fruit, vegetables, soups and yoghurt, for example, can contain substantial amounts of water.
So a recommendation of 2 litres does not necessarily mean drinking 2 litres of additional plain water.
Why Can Two People Need Very Different Amounts?
Our bodies continuously lose water through urine, breathing, the skin and bowel movements.
How much we need to replace depends on many factors.
Exercise and sweating increase water loss. Hot weather can increase requirements considerably. Body size, diet, pregnancy and breastfeeding also influence water needs.
Illness matters too. Fever, vomiting and diarrhoea can rapidly increase fluid loss.
Age is another factor.
As we get older, the sensation of thirst can become less reliable, while the kidneys’ ability to concentrate urine may change. This means some older adults may not feel particularly thirsty even when they need more fluid.
Can You Trust Your Thirst?
For most healthy adults in ordinary conditions, thirst is an important and effective biological signal.
The brain continuously monitors the concentration of body fluids. When water availability falls, thirst increases and the kidneys begin conserving water.
But thirst is not perfect in every situation.
Older age, intense exercise, very hot environments, illness and some medications can make relying on thirst alone less dependable.
Urine can provide another practical clue. Persistently very dark, concentrated urine may suggest that more fluid is needed, although urine colour is influenced by foods, supplements, medications and medical conditions and is not a diagnostic test by itself.
Is More Water Always Better?
No.
The body needs water balance, not the maximum possible amount of water.
Drinking far more than the kidneys can remove can dilute sodium in the blood and cause hyponatraemia, which can become dangerous.
And some people with heart failure, advanced kidney disease or other medical conditions may need specific limits on fluid intake.
This is why hydration should not become a competition to reach an arbitrary number of litres.
What Is the Best Everyday Approach?
For most healthy people, the practical goal is straightforward:
drink regularly, respond to thirst and increase fluids when water losses increase.
Pay more attention during exercise, hot weather and illness, and as you get older.
Water requirements are individual. What matters for healthy aging is not achieving a fashionable target but maintaining the water balance that allows your circulation, kidneys, brain and cells to function normally.
Based on Research
Yamada Y, Zhang X, Henderson MET, et al. Variation in human water turnover associated with environmental and lifestyle factors. Science. November 2022.
