Why drinking enough water matters
Fluid needs, effects of dehydration and practical tips
Water is the essential foundation for nearly all bodily functions: it regulates body temperature, transports nutrients and oxygen, removes metabolic waste products via the kidneys and skin, protects joints and organs, and is indispensable for digestion and cellular metabolism. The human body is 55–75% water. Even a fluid deficit of 1–2% of body weight can measurably impair concentration, mood and physical performance.
Our calculator uses the rule of thumb of 35 ml per kilogram of body weight as the base requirement, which corresponds to the recommendation of many nutrition scientists. An 80 kg person therefore needs at least 80 × 35 ml = 2,800 ml = 2.8 liters daily. Adding the activity surcharge for sports increases this to 3.3–3.8 liters. These figures refer to total fluid intake from drinks; water from solid food (approx. 500–700 ml with a balanced diet) comes on top.
Special population groups have different needs: pregnant and breastfeeding women need an additional 300–600 ml daily. Older adults often drink too little because the sensation of thirst decreases with age – deliberately scheduling drinking breaks is advisable here. Athletes doing long sessions should also take in electrolytes (sodium, potassium, magnesium) alongside water to avoid hyponatremia. People with kidney or heart conditions should discuss their individual fluid intake with their doctor, as too much fluid can be harmful.
Practical tips for drinking enough: start the day with a large glass of water. Always keep a bottle within reach. Use reminders on your smartphone or a drinking app. Flavor water with cucumber, lemon or mint if plain water is too bland for you. Unsweetened herbal teas and sparkling water also count fully towards your fluid intake. Pay attention to the color of your urine: pale yellow signals good hydration, darker urine indicates a fluid deficit.