Water Intake Calculator

Why Hydration Matters

Water is the most essential nutrient — you can survive weeks without food but only days without water. It makes up approximately 60% of total body weight in adults and is involved in virtually every physiological process: nutrient transport, temperature regulation, joint lubrication, digestion, waste removal, and cognitive function.

Even mild dehydration of 1–2% body weight loss has been shown to impair cognitive performance, reduce exercise capacity, increase perception of effort, and negatively affect mood. At 3–4% dehydration, physical performance drops significantly. Adequate hydration is one of the simplest, most impactful health habits available.

How to Use This Water Intake Calculator

Enter your bodyweight, select your climate, and choose your exercise level for today. Your personalised daily water target updates instantly — displayed in litres, number of 250ml glasses, and 500ml bottles. The calculator also shows an hourly reminder schedule and the extra water needed for your climate and exercise.

How Your Daily Water Target is Calculated

A 70kg person in a moderate climate who exercises for 30 minutes needs approximately: (70 × 35) + 250 + 350 = 3,050ml (3.1 litres) per day. Note that food also contributes approximately 20% of daily water intake, so the body's total water requirement is partially met through solid food.

Signs of Dehydration

• Urine colour: The simplest indicator. Pale yellow = well hydrated. Dark yellow or amber = drink more. Clear may indicate over-hydration.
• Thirst: By the time you feel thirsty, you are already mildly dehydrated. Thirst is a lagging signal — do not wait for it.
• Headache: One of the earliest signs of dehydration, often mistaken for other causes.
• Fatigue and brain fog: Mild dehydration impairs concentration and increases mental fatigue.
• Decreased urine output: Urinating fewer than 4 times per day suggests inadequate intake.

Hydration and Exercise

During exercise, the body loses water through sweat — a rate that can range from 0.5 litres per hour in mild conditions to over 2 litres per hour during intense exercise in heat. For sessions under 60 minutes, water is sufficient. For sessions over 60 minutes, particularly in heat, an electrolyte source (sodium, potassium, magnesium) becomes important to prevent hyponatraemia — a dangerous drop in blood sodium caused by drinking large amounts of plain water without electrolyte replacement.

Tips for Hitting Your Daily Water Target

• Start every morning with 500ml of water before coffee or food
• Keep a 1-litre water bottle visible on your desk — visual cues dramatically increase intake
• Set hourly phone reminders using the schedule from our calculator
• Drink a glass of water before every meal — it also supports appetite regulation
• Flavour water with lemon, cucumber, or mint if plain water feels unappealing
• Count herbal teas and sparkling water toward your daily total — they hydrate equally

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