We have all heard the advice to drink "eight glasses of water a day". It is a memorable starting point, but not everyone needs the same amount. Age, body weight, physical activity, air temperature and health status all directly affect how much fluid we need.

What does the body use water for?

Water makes up a large part of our body weight and plays a role in almost every vital process:

Regulating body temperature,
Carrying nutrients to cells,
Keeping digestion and bowel movements regular,
Protecting joints and tissues,
Removing waste products through the kidneys.

Throughout the day we lose water through sweat, breathing and urine, and we need to replace it with drinks and food.

Factors that affect water needs

Body weight

A commonly used practical approach for healthy adults is to estimate around 30-35 ml of fluid per kilogram of body weight. For an adult weighing 60 kg, this corresponds to about 1.8-2.1 litres of fluid a day. This is a rough estimate and may vary with your personal circumstances.

Physical activity

Fluid lost through sweat during exercise increases with the length and intensity of training. On exercise days, extra fluid is needed before, during and after training.

Weather and environment

Fluid loss can increase in hot and humid weather, at high altitude and in air-conditioned rooms.

Special life stages

Fluid needs rise during pregnancy and breastfeeding. Fluid loss also increases with fever, diarrhoea and vomiting; in these situations it is important to follow your physician's advice.

If you have a condition that requires fluid restriction, such as heart or kidney disease, always set your daily fluid intake together with your physician.

Does only water count?

Our daily fluid intake is not made up of water alone. Ayran, milk, herbal teas, soups and water-rich fruit and vegetables also contribute. Foods such as cucumber, watermelon, tomatoes and lettuce are mostly water.

Sugary drinks and fruit juices, however, provide extra energy and sugar. The World Health Organization recommends limiting free sugar intake, so making water your main source of fluid is a good choice. Tea and coffee also contribute to fluid intake, but it is worth keeping an eye on the amount of caffeine.

How can I tell whether I am drinking enough?

A simple indicator is the colour of your urine. A pale straw colour generally suggests adequate fluid intake. Dark urine, headaches, tiredness and a dry mouth may suggest that you need to drink more. Bear in mind that some vitamin supplements and medications can change urine colour.

Thirst is also an important signal. However, since the sense of thirst can weaken in older adults, drinking at regular intervals is even more important for this age group.

Practical tips for making water a habit

Start your day with a glass of water.
Always keep a water bottle on your desk or in your bag.
Drink a glass of water with every meal.
Set reminders on your phone or use a water tracking app.
If you do not enjoy plain water, flavour it with lemon, mint, cucumber slices or a cinnamon stick.
Use a marked bottle to keep track of how much you drink during the day.

Frequently asked questions

Can drinking too much water be harmful?

In healthy people, the kidneys can remove excess water. However, drinking a very large amount in a very short time can, rarely, cause problems. Spreading your intake across the day at regular intervals is the safest approach.

Can mineral water replace water?

Mineral water contributes to fluid intake and contains minerals. However, its sodium content varies by brand, so people on a salt-restricted diet in particular are advised to check the label.

You can use the water needs calculator on this website to get an approximate estimate. The result is a general estimate; for a personal assessment you can consult a dietitian or your physician.

How to work out your daily water needs