“Drink eight glasses of water a day” is one of the most repeated pieces of health advice — and it’s also an oversimplification. Your actual hydration needs depend on your body size, activity level, climate, and diet.
A More Useful Starting Point
Rather than fixating on a universal number, a helpful baseline is to drink enough fluid that your urine is pale yellow for most of the day, and to drink water regularly rather than waiting until you feel very thirsty — thirst is a signal that you’re already somewhat behind on fluids.
Factors That Increase Your Needs
- Exercise, especially in heat or for longer durations
- Hot or humid weather
- Pregnancy and breastfeeding
- Illness involving fever, vomiting, or diarrhea
- High-sodium or high-protein diets
You Don’t Only Get Fluids From Water
Water-rich foods — like fruits, vegetables, soups, and yogurt — contribute meaningfully to daily hydration. Beverages like tea and coffee also count toward fluid intake for most people, despite the old myth that caffeine causes significant net fluid loss.
Signs You May Need More Fluid
- Dark yellow urine
- Headaches or fatigue that improve after drinking water
- Dry mouth or unusual thirst
- Dizziness, particularly when standing up quickly
If you have a heart, kidney, or liver condition that affects fluid balance, follow your healthcare provider’s specific guidance rather than general hydration advice like this article.