Water makes up about 60% of an adult's body weight and is involved in almost every physiological process — from temperature regulation, through nutrient transport, to kidney function. Proper hydration affects concentration, performance and well-being. So how much should we really drink each day?
General Recommendations
The European Food Safety Authority (EFSA) recommends a fluid intake of about 2.0 litres for women and 2.5 litres for men per day. These values include fluids from all sources, including food, which provides about 20–30% of water.
A Simple Formula for Your Needs
A popular and practical conversion is 30–35 ml of water per kilogram of body weight:
Requirement [ml] = body weight [kg] × 30 to 35
Calculation Example
A person weighing 70 kg needs:
- Lower bound: 70 × 30 = 2100 ml
- Upper bound: 70 × 35 = 2450 ml
The daily requirement is therefore about 2.1–2.5 litres. This is a baseline value for moderate activity and climate — in heat or during training it increases.
When You Need More Water
- Physical exertion — an extra 0.5–1 litre for each hour of intense training
- Heat and high temperature — greater losses through sweat
- Fever, diarrhoea, vomiting — increased fluid losses
- Pregnancy and breastfeeding — greater demand on the body
- High-protein or high-fibre diet — the body needs more water
Signs of Dehydration
Even a 1–2% loss of body water lowers performance and concentration. Warning signs include: thirst, dark urine, dry mouth, headache, fatigue and dizziness. A good indicator of hydration is urine colour — pale straw means proper hydration, while dark yellow signals a shortfall.
Can You Drink Too Much?
Yes — though rarely. Excessive water intake over a short time can lead to hyponatraemia, a dangerous dilution of sodium in the blood. This mainly affects endurance athletes drinking very large amounts of plain water. In everyday life the risk is minimal.
Practical Tips
- Drink a glass of water right after waking up
- Keep a bottle in sight at your desk
- Drink regularly, without waiting for the feeling of thirst
- Fruit and vegetables (cucumber, watermelon, tomato) also hydrate
Remember
The figures given are approximate values for healthy adults. In cases of kidney or heart disease or when taking diuretics, your requirement is set individually by a doctor.
Want to find out your daily norm? Enter your body weight and activity level in our hydration calculator on liczbnik.pl and it will calculate the recommended amount of water for you.