Calculate your daily water needs
Enter your details and instantly calculate your personal recommended daily water intake.
How much water do you need each day?
The well-known guideline of ‘eight glasses of water a day’ is a handy reminder, but it is not an exact science. Your actual water requirements depend on your body weight, how much you exercise and the environment in which you live. A commonly used rule of thumb is approximately 30 to 35 millilitres of water per kilogram of body weight per day. By way of comparison, the European Food Safety Authority (EFSA) recommends 2.0 litres of water per day for adult women and 2.5 litres for men, from both drinks and food combined.[1]
For someone weighing 70 kilos, that works out at roughly 2.1 to 2.5 litres a day. Do you exercise intensively or is the weather hot? If so, your fluid requirements are higher. Important to note: this includes all the fluid you consume, including tea, coffee and water-rich foods such as fruit and vegetables.
Please note: these figures are general guidelines for healthy adults. If you have a kidney or heart condition, are taking certain medicines, or are pregnant, please consult your GP or doctor about the right amount of fluid for your situation.
Calculating water intake: what is the calculator based on?
Our calculator is based on the rule of thumb of 30 to 35 ml per kilogram of body weight, with an adjustment for your activity level and extra fluid if you use weight medication. That question is set to Yes by default; if you do not use weight medication, choose No. The more active you are, the more fluid you lose through sweat and breathing. You also lose more fluid in a hot or humid environment, or at high altitude. The calculator does not take this into account, so drink a little more than the result in those situations. By way of comparison, the European Food Safety Authority (EFSA) advises adults to have around 2.0 (women) to 2.5 litres (men) of fluid a day, from food and drinks combined.
This result is an indication only. Fat tissue contains far less water than muscle tissue. With a higher body weight, a calculation based on your total weight may therefore come out too high[6]. That also applies to this calculator. The EFSA advice is then a more realistic starting point.
If you have a condition where you need to watch your fluid intake, such as a heart, kidney or liver condition, consult your doctor or dietitian before you start drinking more.
You will see the result in litres per day, and also in 250 ml glasses and 0.5 litre bottles. This gives you a specific target to work towards. Think of it as a starting point: listen to your body and keep an eye on the colour of your urine (light yellow is a good sign).
Why is drinking water so important?
Your body is made up of around 60% water.[2] That fluid is involved in virtually everything your body does. Drinking enough water helps, amongst other things, to maintain a healthy body temperature by enabling you to sweat and cool down, the transport of nutrients and oxygen to your cells, smooth digestion and the prevention of constipation, the elimination of waste products via your kidneys, and healthy, supple joints and skin. Even a slight fluid deficit of 1 to 2 per cent can cause headaches, tiredness and reduced concentration.[3]
Water and weight loss: what’s the link?
Water can help with weight loss in several ways. Firstly, a large glass of water before a meal can make you feel fuller, so you eat less. In a small study of people aged 55 to 75 with overweight, all participants followed a calorie-restricted diet for twelve weeks. Those who drank half a litre of water before each meal lost around 2 kilos more than those who followed the diet alone.[4]
What’s more, water contains zero calories. A glass of fizzy drink or fruit juice easily contains 100 kcal or more. If you replace sweetened drinks with water, you’ll save calories without having to go on a ‘diet’.
Drinking water when taking weight medication
Are you taking weight medication? If so, it is particularly important to drink plenty of fluids. This medication suppresses your appetite, and because you eat less, you also consume less fluid from your diet. Common side effects such as nausea, vomiting and diarrhoea can also cause dehydration. The advice is therefore to drink plenty of fluids, especially if you have kidney problems. If you experience severe or persistent side effects and are unable to keep fluids down, or if you notice signs of dehydration (such as extreme thirst, dark-coloured urine, dizziness, or reduced urination), contact your treating physician or general practitioner immediately. Dehydration caused by gastrointestinal symptoms can, in rare cases, worsen kidney function. In the event of constipation, our doctors also advise drinking plenty of water. If you answer Yes to the weight medication question in the calculator, it adds extra fluid to help prevent dehydration from these side effects. Sip water throughout the day. If you have a heart, kidney or liver condition requiring fluid restriction, do not increase your fluid intake without consulting your doctor.
Good to know: drinking water alone won’t make you lose weight. It is a valuable aid as part of a healthy diet and sufficient exercise. In cases of persistent excess weight, a medically supervised programme may offer a solution.
7 practical tips for staying hydrated
Please note: The result from this calculator is for guidance only. Because fat tissue contains far less water than muscle, calculators using total body weight tend to overestimate fluid targets for individuals with a high body weight[6]. If you have a condition where fluid or dietary intake must be managed (such as heart, kidney, or liver disease), do not follow high-end estimates without consulting your doctor or dietitian first. Standard EFSA guidelines (around 2.0 to 2.5 litres daily from foods and fluids combined) offer a safer baseline reference for most adults.
Frequently asked questions about water intake
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For healthy adults, a rule of thumb is approximately 30 to 35 ml of water per kilogram of body weight. For most people, this amounts to around 1.5 to 2.5 litres a day. During intensive exercise or in hot weather, the requirement is higher. Use the calculator at the top of this page for an estimate tailored to your weight and activity level.
Yes. For a long time, it was thought that coffee and tea actually caused dehydration because of their caffeine content, but when consumed in moderation, they actually contribute to your overall fluid intake.[5] Water from food, such as soup, vegetables and fruit, also counts towards your total intake. Water remains the best choice, however, as it contains no calories, sugar or caffeine.
In rare cases, yes. If you consume extremely large quantities in a short space of time, the sodium concentration in your blood may drop too low. This is called hyponatraemia and can be dangerous. For most people, this is not a risk if they drink normally. Spread your fluid intake throughout the day rather than drinking a large amount all at once, and listen to your body’s thirst signals.
Water can help with weight loss. Drinking a glass of water before a meal helps you feel fuller, effectively replaces high-calorie beverages, and assists in lowering overall calorie intake during the meal. Water on its own won’t make you lose weight, but it is a valuable habit as part of a healthy diet and exercise routine.
The colour of your urine is the simplest indicator: pale yellow means you are well hydrated, whilst dark yellow suggests you are not drinking enough. Other signs of dehydration include thirst, headaches, tiredness, a dry mouth and reduced concentration.
Yes. When exercising, you lose fluid through sweat and faster breathing. As a rule of thumb, you should drink extra water before, during and after exercise. If you’re doing intensive exercise for more than an hour and sweating heavily, a sports drink can be a good way to quickly replenish fluids and energy.
Absolutely. In a hot or humid climate, you sweat more to cool down, which increases your fluid loss. If you are travelling to or staying at high altitudes (above 2,500 metres), you should increase your fluid intake slightly. The combination of more rapid breathing in drier air and increased respiration causes additional fluid loss. The calculator does not take hot weather or altitude into account, so drink a little more than the result in those situations.
It’s a good habit. Whilst you’re asleep, you don’t consume any fluids for hours, even though you do lose fluids through your breath and skin. A large glass of water when you get up helps to replenish those fluids. It isn’t essential, though. What’s more important is that you drink enough throughout the day.
Flavouring water with fresh cucumber, lemon, mint or a few berries is a great and healthy way to drink more. Do be careful with ready-made flavoured drinks and syrups, though: these often contain added sugars or sweeteners. So flavouring your water yourself is the better choice.
It is wise to pay close attention to this. Weight medication suppresses your appetite, which also means you consume less fluid from your food. Side effects such as nausea, vomiting and diarrhoea can also lead to dehydration. The advice is therefore to drink plenty of fluids, spread out over the course of the day. Answer Yes to the weight medication question in the calculator for a slightly more generous guideline, and if in doubt, consult your healthcare professional. If you have a heart, kidney or liver condition requiring fluid restriction, do not increase your fluid intake without consulting your doctor. If you are unable to keep fluids down, or if you notice signs of dehydration (such as extreme thirst, dark-coloured urine, dizziness, or reduced urination), contact your treating physician or general practitioner immediately.
No, this calculator is intended for healthy adults. Children have different needs in relative terms, and older people often experience a reduced sense of thirst, which means they can become dehydrated more quickly. For these groups, and in the case of pregnancy or certain medical conditions, it is advisable to seek personalised advice from a doctor or dietitian.
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