How Much Water Should You Drink a Day? (By Weight and Activity)

The Simple Formula: 30-35ml Per Kilogram of Body Weight

The most practical guideline for daily water intake is 30-35 millilitres per kilogram of body weight. A 60kg person needs approximately 1.8-2.1 litres. A 75kg person needs about 2.3-2.6 litres. A 90kg person needs roughly 2.7-3.2 litres. A 100kg person needs approximately 3.0-3.5 litres.

These are baseline amounts for moderate climates and light activity. Active people, those in hot climates, and pregnant or breastfeeding women need more.

The commonly cited "8 glasses a day" rule (approximately 2 litres) is a reasonable average for a 60-65kg sedentary person in a temperate climate. But it has no scientific origin — it appears to derive from a 1945 US Food and Nutrition Board recommendation that was taken out of context. The original recommendation noted that most of this water would come from food, not just drinking.

Why Hydration Matters for Health and Weight

Water is involved in virtually every biological process in your body. It transports nutrients, regulates temperature, cushions joints, removes waste products, and supports every organ system. Even mild dehydration (1-2% of body weight) impairs cognitive function, mood, and physical performance.

For weight management specifically, water plays several important roles. Drinking water before meals has been shown to reduce calorie intake by 75-90 calories per meal in studies published by the National Institutes of Health. Over three meals per day, that is 225-270 fewer calories, enough to produce noticeable weight loss over weeks without any other dietary changes.

Water also has a modest thermogenic effect. Drinking 500ml of cold water temporarily increases metabolic rate by 24-30% for about 60 minutes as your body expends energy to heat the water to body temperature. This burns an additional 50-100 calories per day if you drink 2 litres of cold water. Read our guide on foods that boost metabolism for more on this effect.

Perhaps most importantly, thirst is frequently misinterpreted as hunger. Many people reach for food when their body is actually signalling a need for water. Drinking a glass of water when you feel hungry, then waiting 15 minutes before eating, can help distinguish genuine hunger from thirst and prevent unnecessary snacking.

How to Know If You Are Drinking Enough

The simplest indicator is urine colour. Pale yellow (like lemonade) indicates adequate hydration. Dark yellow or amber indicates dehydration. Clear and colourless may indicate overhydration, though this is rarely a concern for most people.

Other signs of dehydration include persistent thirst, dry mouth, fatigue and low energy, headaches (especially in the afternoon), dizziness when standing up quickly, decreased urination frequency, and dry skin. The Mayo Clinic notes that chronic mild dehydration is extremely common, particularly in older adults whose thirst sensation diminishes with age.

Does Coffee and Tea Count?

Yes. Despite the persistent myth that caffeine dehydrates you, moderate coffee and tea consumption contributes to your daily fluid intake. The diuretic effect of caffeine is mild and does not offset the water consumed in the beverage. A cup of coffee is approximately 95% water. The British Dietetic Association confirms that tea and coffee count towards daily fluid intake.

However, sugary drinks, juice, and alcohol are different. Sugary drinks add substantial calories (140-200 per glass) alongside fluid. Alcohol has a stronger diuretic effect that can worsen dehydration. Water, unsweetened tea, and black coffee remain the best hydration choices for health and weight management.

For a zero-calorie Nigerian option, try unsweetened zobo (hibiscus drink) — refreshing, rich in antioxidants, and hydrating.

Practical Tips for Drinking More Water

Carry a water bottle and refill it throughout the day. Drink a glass of water immediately upon waking (your body is dehydrated after 7-8 hours of sleep). Have a glass before each meal. Set phone reminders if you frequently forget to drink. Flavour water with lemon, cucumber, mint, or ginger if you find plain water boring. Eat water-rich foods: cucumbers (96% water), watermelon (92%), oranges (87%), and lettuce (96%) all contribute to hydration.

Read our calorie deficit guide for how proper hydration supports weight loss, or use the food search tool to check the water content of any food.

Hydration needs vary by individual. People with kidney disease, heart conditions, or those taking certain medications should consult their doctor about appropriate fluid intake.