How much water should you drink a day?
The DGE (German Nutrition Society) specifies 1,410 ml a day from drinks, plus 2,600 ml total intake. Here is how to calculate your needs and find out when more is necessary.
A healthy adult between 25 and 50 years of age should consume 1,410 ml of water a day from drinks. That is the guideline value of the Deutsche Gesellschaft für Ernährung (DGE, German Nutrition Society). Adding the water from solid food and metabolism results in a total water intake of 2,600 ml. Exercise, heat, age and illness sometimes shift this requirement considerably.
Guideline values by age
For adults, the DGE specifies between 1,230 and 1,470 ml of water a day from drinks, graded by age group. Depending on age, the total water intake is 2,250 to 2,700 ml. It also includes the water from solid food and the oxidation water that is produced by the metabolism itself.
| Age group | Water from drinks | Total water intake |
|---|---|---|
| 19 to under 25 years | 1,470 ml | 2,700 ml |
| 25 to under 51 years | 1,410 ml | 2,600 ml |
| 51 to under 65 years | 1,230 ml | 2,250 ml |
| 65 years and older | 1,310 ml | 2,250 ml |
According to the DGE, these values apply with an energy intake that meets requirements and under average living conditions. They do not include any allowance for exercise or heat.
The popular rule of thumb of two litres a day is slightly above the DGE guideline value for drinks. It remains within a plausible range. More important than the exact figure is how you spread your intake over the day.
Calculating water needs: formula and example values
The common formula works with 30 to 35 ml per kilogram of body weight per day. For 70 kg, that equals 2.1 to 2.45 litres. For context: this rule is a practical heuristic from nutritional counselling. It is not endorsed by any professional society.
A review in the European Journal of Clinical Nutrition shows why. The various ml-per-kilogram formulas are based on inconsistent older estimates. Depending on the variant, they produce significantly different results. The formula is useful as a rough guide.
| Body weight | 30 ml/kg | 35 ml/kg |
|---|---|---|
| 50 kg | 1.50 l | 1.75 l |
| 60 kg | 1.80 l | 2.10 l |
| 70 kg | 2.10 l | 2.45 l |
| 80 kg | 2.40 l | 2.80 l |
| 90 kg | 2.70 l | 3.15 l |
| 100 kg | 3.00 l | 3.50 l |
Calculator
Your personal water requirement
Your daily drinking amount
ca. 1,4 – 1,6 litres
Rule of thumb as a rough guide – needs are higher with exercise, heat or illness.
A common mistake with this calculation: the values refer to total water intake, not the amount you drink. You take in around a third of it through solid food and metabolism. If the formula gives you 2.4 litres, you drink about 1.6 litres of it.
Which factors change your water needs
Six factors determine how much your needs deviate from the guideline value:
- Physical activity: Sweating is the largest variable source of loss. Intensive training increases your needs significantly.
- Ambient temperature: Heat increases your needs even without exercise. Dry heated indoor air in winter has a similar effect.
- Age: The sense of thirst decreases with age. Older people therefore often drink too little.
- Diet: Fruit and vegetables cover part of your needs. With a low-water diet, the amount you need to drink increases.
- Alcohol: Alcohol inhibits the antidiuretic hormone (ADH) and increases urine output.
- Illness: Fever, diarrhoea and vomiting greatly increase your needs. In the case of heart and kidney disease, on the other hand, fluid intake is restricted by a doctor.
Incidentally, coffee and tea do not dehydrate the body. This assumption is considered to have been disproved. Both count towards your fluid balance.
How much to drink in hot weather?
In hot weather, your needs increase because the body releases heat through sweating. At high temperatures and with physical activity, sweat loss can amount to several litres a day. Spread the extra amount over the day instead of drinking it in a few large portions.
Two points are relevant in practice. Firstly, thirst often kicks in late in hot weather, especially in older people. Secondly, electrolytes are lost with sweat, especially sodium. If you sweat heavily for hours and replace the fluid only with plain water, you dilute your sodium level.
On hot days, therefore, pay attention to both: a sufficient amount and sodium intake through food or suitable drinks.
Fluid intake during exercise
During exercise, the amount you drink depends on your sweat loss, not on a fixed daily amount. The simplest method of measurement is the scales: weigh yourself before and after training. Every kilogram lost corresponds to around one litre of fluid.
The sports scientist Andy Galpin has proposed a rule of thumb for this, which has become known as the Galpin Water Equation. Converted to metric units, it reads: body weight in kilograms times 2 gives the millilitres to drink every 15 minutes during exercise. At 75 kg, that is around 150 ml per quarter of an hour. In hot weather, Galpin recommends adding extra.
This formula, too, comes from sports science practice, not from a guideline. It is suitable as a starting value that can be adjusted to the actual loss using the scales.
What happens if you don't get enough fluids?
Even a water loss of 1 to 2% of body weight measurably impairs performance. This is summarised in a review article in the journal of the American College of Sports Medicine (ACSM). Concentration, reaction time, short-term memory and mood are affected.
Typical early signs are:
- Tiredness and declining concentration
- Headaches
- Dark urine
- Dry mucous membranes
In old age, these early warning signs are weaker. A lack of fluids then goes unnoticed for longer and can lead to confusion or circulatory problems. For older people, drinking regularly according to a plan therefore makes more sense than waiting until they are thirsty.
Severe fluid loss is a medical emergency. From a loss of around 10 to 15% of body weight, it is considered life-threatening and requires medical treatment.
Can you drink too much water?
Yes. At rest, the kidneys of a healthy adult excrete around 800 to 1,000 ml of water per hour. If you drink significantly more than this over several hours, you overload this capacity. The sodium level in the blood falls, resulting in hyponatraemia, colloquially known as water intoxication.
Possible symptoms include:
- Headaches
- Nausea and vomiting
- Confusion and difficulty concentrating
- Muscle cramps
- Seizures, up to and including loss of consciousness
- Breathing problems
The phenomenon was first described in endurance athletes who drank large quantities of plain water during long competitions. In the specialist literature, it is referred to as exercise-associated hyponatraemia. In everyday life, the risk is low. It becomes relevant with very large quantities in a short time, with extreme endurance exertion and with impaired kidney function.
People with heart or kidney disease should agree on their fluid intake with their doctor. For them, both too little and too much can be problematic.
Drinking enough regularly
Most people fall short on distribution, not on quantity. If you only notice in the evening that you have barely drunk anything, you rarely make up for it sensibly. Five approaches help:
Keep water in sight
- A filled bottle at your workplace is a more reliable reminder than a good intention.
- Link it to routines: One glass with every meal, one after getting up and one before going to bed already adds up to around one litre.
- Improve the taste: Lemon, cucumber, mint or ginger make water more pleasant without adding sugar.
- Plan in water-rich foods: Cucumber, watermelon, tomatoes and citrus fruits make a measurable contribution to your fluid balance.
- Drink before, during and after exercise: In other words, before you get thirsty.
If you find the taste of your tap water off-putting, you can tackle this in a targeted way. An activated carbon filter reduces chlorine and other substances that spoil the taste. Minerals such as calcium and magnesium remain in the water. What else is in tap water is covered in the guide Substances in tap water. The article How do you measure water quality? explains how to check the values for your own address.
Related to this topic
Alb Filter FUSION – fresh water straight from the tap
If you like your drinking water, you automatically drink more of it. The FUSION under-sink drinking water filter delivers freshly filtered tap water right at the tap – activated carbon block and Nano ultrafiltration, without electricity and without wastewater.
Frequently asked questions
How much water should I drink per day?
According to the DGE guideline values, 1,230 to 1,470 ml per day from drinks, depending on age. For 25- to 50-year-olds, it is 1,410 ml. The requirement is higher with exercise, heat or fever.
How do I calculate my individual water requirement?
A rough guide is 30 to 35 ml per kilogram of body weight. For 70 kg, that is 2.1 to 2.45 litres of total water intake. Around a third of this comes from solid food and metabolism. The formula is a practical rule of thumb, not a recommendation from a professional society.
Do coffee and tea count towards fluid intake?
Yes. The earlier assumption that coffee dehydrates the body is considered disproven. Both drinks count towards your fluid balance.
How much should you drink in summer?
In hot weather, sweating increases the requirement by several hundred millilitres up to several litres, depending on temperature and activity. Spread the amount across the day. If you sweat heavily, also pay attention to sodium.
Can you drink too much water?
Yes. At rest, the kidneys excrete about 800 to 1,000 ml per hour. Anyone who drinks significantly more than this over several hours risks hyponatraemia, with headaches, nausea and, in severe cases, seizures. This rarely happens in everyday life, but is more common during extreme endurance exercise.
How can I tell that I haven't drunk enough?
From tiredness, headaches, declining concentration and dark urine. Measurable effects already occur with a water loss of 1 to 2%. In older age, these signals are weaker.
How much should I drink during exercise?
It depends on your sweat loss. Weigh yourself before and after training: every kilogram lost corresponds to about one litre. A starting value during exercise is around 2 ml per kilogram of body weight every 15 minutes.
How much water does an older person need?
For people aged 65 and over, the DGE specifies 1,310 ml from drinks and 2,250 ml of total water intake. Because the sense of thirst diminishes with age, a fixed drinking schedule makes more sense than waiting to feel thirsty.
Sources
- Deutsche Gesellschaft für Ernährung (German Nutrition Society): Reference values for water intake. https://www.dge.de/wissenschaft/referenzwerte/wasser/
- Vivanti, A.P. (2012): Origins for the estimations of water requirements in adults. European Journal of Clinical Nutrition 66(12), 1282 to 1289. https://www.nature.com/articles/ejcn2012157
- Riebl, S.K. and Davy, B.M. (2013): The Hydration Equation. Update on Water Balance and Cognitive Performance. ACSM's Health and Fitness Journal. https://pmc.ncbi.nlm.nih.gov/articles/PMC4207053/
- StatPearls (National Institutes of Health): Adult Dehydration. https://www.ncbi.nlm.nih.gov/books/NBK555956/
