How much water should you drink a day?
Daily fluid needs from trusted reference values, how heat and exercise change them, signs you need more, and when drinking a lot can be harmful.
By the Fitlyn editorial team · Published · 2 min read
"Eight glasses a day" is easy to remember, but your real needs depend on your body, the climate, your activity and what you eat. Here is what the reference values say and how to apply them.
The reference values
Health authorities give adequate intakes for total water from all drinks and food:
| Source | Women | Men |
|---|---|---|
| European Food Safety Authority (EFSA) | about 2.0 L a day | about 2.5 L a day |
| US National Academies | about 2.7 L a day | about 3.7 L a day |
These totals include water from food, which provides roughly 20% of the total for many people (more if you eat a lot of fruit, vegetables and soups). So, from drinks alone, many adults need roughly 1.6 to 2 L (women) and 2 to 3 L (men) on a typical day in a mild climate.
When you need more
- Heat: in hot climates you can lose a lot of fluid through sweat, even without exercising.
- Exercise: drink before, during and after activity. For long or intense sessions in the heat, you may also need to replace salt.
- Illness: fever, vomiting and diarrhoea increase fluid losses. Oral rehydration solutions are helpful for diarrhoea.
- Pregnancy and breastfeeding: needs are higher (EFSA suggests about 300 ml more a day in pregnancy and 600 to 700 ml more while breastfeeding).
Simple ways to check
- Urine colour: pale yellow usually means you are drinking enough. Dark yellow suggests you need more.
- Thirst: for most healthy adults, drinking when thirsty works well. Older adults may feel thirst less, so regular drinking matters more for them.
What counts towards your fluids?
Water is the best everyday choice. Milk, laban, tea and coffee also count. Moderate amounts of caffeine do not dehydrate you overall. Juices and sweetened drinks count as fluid, but they add sugar and calories, so keep them small.
Can you drink too much?
Yes, although it is uncommon. Drinking very large amounts in a short time can dilute the sodium in your blood (hyponatraemia). This mostly happens in endurance events when people drink far beyond their sweat losses. It can be dangerous.
Tips to drink enough
- Keep a refillable bottle with you and refill it at set times.
- Drink a glass of water with each meal.
- Flavour water with lemon, mint or cucumber instead of sugar.
- Eat water-rich foods such as watermelon, cucumber, oranges and soups.
- In Ramadan, spread your drinks between iftar and suhoor instead of drinking a lot at once.
How Fitlyn helps
Fitlyn tracks your water with one tap, in millilitres or fluid ounces, and can remind you through the day. Your daily water also shows in your weekly report.
Sources
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on Dietary Reference Values for water. EFSA Journal, 2010.
- Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate, 2005.
- Killer SC, et al. No evidence of dehydration with moderate daily coffee intake. PLOS ONE, 2014.
