In 30 seconds
- The European Food Safety Authority considers 2 litres of water a day adequate for women and 2.5 for men, including the water that comes from food.
- As food provides 20-30%, 1.4-1.6 litres from drinks is usually enough if you are a woman and 1.75-2 litres if you are a man.
- The 8-glasses rule has no scientific basis. Coffee and tea count too.
- Thirst and the colour of your urine are good guides. If you exercise, add what you lose in sweat.
“Drink two litres a day” is probably the most repeated piece of health advice. There is some truth in it, but it is often misunderstood. This is what the official recommendations and the studies say.
Daily water according to EFSA
What you drink is only part of the day's water
What EFSA recommends
In 2010, the European Food Safety Authority set the adequate water intake for adults 1:
| Total water | Of which, from drinks | |
|---|---|---|
| Women | 2.0 L | 1.4-1.6 L |
| Men | 2.5 L | 1.75-2.0 L |
| Pregnancy | 2.3 L | 1.6-1.8 L |
| Breastfeeding | 2.6-2.7 L | 1.8-2.2 L |
Source: EFSA, 2010. Total water from drinks and food, at moderate temperatures and levels of physical activity. The drinks column assumes food provides 20-30%.
The key lies in the word total: those litres include the water in your food. Fruit, vegetables, soups, yoghurts or a plate of pasta provide 20-30% of the day's water. That is why, from drinks, you normally need quite a bit less than 2 or 2.5 litres.
And these figures are for moderate temperatures and levels of physical activity 1. In the heat or if you exercise, you need more.
The 8-glasses myth
A single figure for everyone makes no sense
The 8-glasses myth
The famous rule of drinking eight glasses of water a day does not come from any study. A review that traced its origin found no scientific basis and pointed out that much of the water we need already comes from food and other drinks 2.
The largest study carried out so far, with more than 5,600 people from 26 countries, measured how much water the body turns over each day and found huge differences: from 1 to 6 litres depending on body size, physical activity, climate and the country's level of development 3. Its authors also conclude that the 8-glasses rule does not hold up. A single figure for everyone makes no sense.
Coffee and tea count too
This is another widespread myth: that coffee dehydrates you. In a study with 50 men used to drinking coffee, four cups a day for three days hydrated them just as well as the same amount of water 4. In another with 72 people, coffee and tea were retained in the body practically as well as water; milk and oral rehydration solution, even better 5.
That does not make every drink a good choice: soft drinks and juices add sugar. But the coffee or tea you have during the day counts towards your water.
How to tell if you are drinking enough
You do not need to count glasses. Three simple signs 7:
- Thirst: if you are thirsty, drink. It is a good guide for most adults.
- Urine colour: pale yellow is ideal. If it is dark, you need more fluid.
- Weight: if you exercise, weighing yourself before and after tells you exactly how much you have sweated.
With age, thirst gives less warning
In older people, thirst responds less well when the body loses fluid, especially in the heat or during exercise, and recovery is slower 6. Day to day they usually drink enough, but in summer or on days when they exercise it is best not to wait until they feel thirsty: carry water with you and drink regularly.
If you exercise
What you can lose in sweat in an hour
If you exercise
On top of your daily amount, add what you lose in sweat, which can range from 0.3 to 2.5 litres per hour. In the sports hydration guide we explain how to measure it with a set of scales, and the hydration calculator gives you an estimate in a minute.
And a word of caution: drinking too much is also a problem. Drinking much more than you sweat, especially in long events, can lower the sodium in your blood and cause hyponatraemia 8.
What about isotonic drinks?
For your everyday life, water. For sessions of more than an hour, especially in the heat, the guidelines recommend a drink with sodium and carbohydrates. Nitrus Isotonic contains five electrolytes, all 13 vitamins, BCAAs and taurine, with a Tropical Punch flavour.
Frequently asked questions
How many litres of water should you drink a day?
The European Food Safety Authority considers 2 litres of total water a day adequate for women and 2.5 for men. As food provides 20-30%, 1.4-1.6 litres from drinks is usually enough for women and 1.75-2 litres for men, at moderate temperatures and activity levels.
Do you need to drink 8 glasses of water a day?
There are no studies to back up that rule. A review that looked for its origin found no scientific basis and pointed out that much of the water you need comes from food and other drinks.
Does coffee dehydrate you?
Not in moderate amounts. In a study with 50 men who drank coffee every day, four cups a day hydrated them just as well as the same amount of water.
How do I know if I am drinking enough water?
Look at two things: if you are not thirsty and your urine is pale yellow, you are most likely well hydrated. If you exercise, weighing yourself before and after tells you how much you have sweated.
How much water should I drink if I exercise?
Your daily amount plus what you lose in sweat, which ranges from 0.3 to 2.5 litres per hour depending on the person, the weather and the intensity. Our hydration calculator gives you an estimate for your case.
Sources
- EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Scientific opinion on dietary reference values for water. EFSA Journal. 2010;8(3):1459. View publication
- Valtin H. «Drink at least eight glasses of water a day.» Really? Is there scientific evidence for «8 x 8»? Am J Physiol Regul Integr Comp Physiol. 2002;283(5):R993-R1004. View publication
- Yamada Y, Zhang X, Henderson MET, et al. Variation in human water turnover associated with environmental and lifestyle factors. Science. 2022;378(6622):909-915. View publication
- Killer SC, Blannin AK, Jeukendrup AE. No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLoS One. 2014;9(1):e84154. View publication
- Maughan RJ, Watson P, Cordery PA, et al. A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index. Am J Clin Nutr. 2016;103(3):717-723. View publication
- Kenney WL, Chiu P. Influence of age on thirst and fluid intake. Med Sci Sports Exerc. 2001;33(9):1524-1532. View publication
- Cheuvront SN, Kenefick RW. Dehydration: physiology, assessment, and performance effects. Compr Physiol. 2014;4(1):257-285. View publication
- Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Br J Sports Med. 2015;49(22):1432-1446. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product. A varied and balanced diet and a healthy lifestyle are important.
