How much water should I drink per day? A complete hydration guide

Water is the main component of the human body — it accounts for 55–70% of body mass — and is essential for almost every physiological process: nutrient transport, temperature regulation, joint lubrication, elimination of metabolic waste and nervous system function.

How much water does an adult need?

The most widely accepted recommendation among nutritionists is 30–40 ml of water per kilogram of body weight per day. For a 70 kg person in a temperate climate with light activity, that works out to about 2.1 litres per day. The WHO sets a minimum of 1.5 litres for adults, but this figure does not account for physical activity or climate.

Factors that increase your fluid needs

• •Intense physical activity: exercise can increase fluid losses by 0.5–2 litres per hour depending on intensity and temperature.
• •Hot or humid climate: sweating increases to regulate body temperature. Add at least 500 ml extra on hot days.
• •High altitude: faster breathing and increased urination raise water losses.
• •Pregnancy and breastfeeding: needs increase by an additional 300–700 ml per day.
• •Fever, vomiting or diarrhoea: extraordinary losses that must be replenished with particular care.

Signs of dehydration

• •Dark yellow or amber urine (the goal is pale yellow or near-clear).
• •Persistent thirst or a dry mouth.
• •Fatigue, difficulty concentrating or headache.
• •Dizziness or light-headedness when standing up.
• •With dehydration > 2% of body weight: drop in physical and cognitive performance.

Does water from food count?

Yes. Approximately 20–30% of total fluid intake comes from solid foods. Fruits and vegetables are especially water-rich: watermelon contains 92%, cucumber 96% and lettuce 95%. However, the calculator refers exclusively to water and drinks you consume, as this is the easiest part to consciously track.

Practical tips for drinking more water

• •Start the day with a glass of water when you wake up, before coffee or breakfast.
• •Always carry a reusable water bottle visible on your desk or in your bag.
• •Link drinking water to habits you already have: before each meal, when you arrive home, etc.
• •Add lemon slices, cucumber or herbs to vary the flavour without adding sugar.
• •Set phone reminders if you tend to forget to drink between meals.