Where the "eight glasses" number came from
It came from a 1945 recommendation that suggested roughly 2.5 litres of water a day for adults, followed by a sentence most people never quote: that most of this quantity is already contained in prepared foods. The second half fell away and the first half became a rule.
Current intake guidance is higher than eight glasses and counts everything. Adequate intake figures commonly cited are around 2.7 litres a day for women from all sources combined, with roughly 20% of that arriving as food rather than drink.
Everything counts, including coffee
Tea and coffee count toward fluid intake. The diuretic effect of caffeine at habitual doses is modest and does not offset the fluid in the cup, which is a persistent myth worth dropping. Milk, soup, and fruit and vegetables with high water content all contribute.
What does not help is treating a target as a ceiling to hit regardless of thirst. Drinking far beyond thirst dilutes blood sodium, and while serious hyponatraemia is rare outside endurance events, forcing litres to meet a number is not a health behaviour.
What changes your needs
- Heat and exercise raise losses through sweat, which is the largest variable for most people.
- Body size, which is why a per-kilogram estimate fits better than a fixed number of glasses.
- Pregnancy and breastfeeding raise requirements.
- Some medicines, including diuretics and SGLT2 inhibitors.
- Fever, vomiting and diarrhoea, where losses rise sharply and quickly.
Hydration in menopause specifically
Two changes matter here and neither is widely discussed. Night sweats and hot flashes increase fluid loss, sometimes substantially in women with frequent vasomotor symptoms, and that loss happens while asleep and unnoticed. Our guide to night sweats covers what reduces them.
Separately, the sensation of thirst blunts with age, so the internal signal that prompts drinking becomes less reliable in later decades than it was earlier. That is an argument for a rough daily habit rather than relying entirely on feeling thirsty.
Dehydration also worsens constipation, which becomes more common after menopause as gut motility slows. If that is the reason you are here, our page on fiber supplements covers the other half of that fix, since fibre without adequate fluid can make constipation worse rather than better.
How to tell whether you are drinking enough
Urine colour is the practical everyday check: pale straw suggests adequate hydration, dark yellow suggests drinking more. Two caveats. B vitamins turn urine bright yellow regardless of hydration, and some medicines change the colour, so the signal is useful rather than definitive.
Persistent dark urine with reduced output, dizziness on standing, or confusion in an older adult are reasons to seek advice rather than simply drink more.