Water Intake Calculator

Proper hydration is fundamental to every bodily function — from regulating temperature and transporting nutrients to cushioning joints and removing waste products. Even mild dehydration (1-2% of body weight) can impair cognitive function, reduce physical performance, cause headaches, and worsen mood. Yet most people chronically underdrink without realising it.

The old advice of "eight glasses a day" is an oversimplification. Your actual water needs depend on your body weight, activity level, climate, diet, and health status. A 90kg person who exercises daily in summer needs significantly more water than a 55kg sedentary person in winter. Our calculator provides a personalised recommendation based on your specific circumstances.

Signs of chronic mild dehydration include dark yellow urine (aim for pale straw colour), persistent headaches, fatigue especially in the afternoon, dry skin, constipation, and feeling hungry when you have recently eaten (thirst is often mistaken for hunger). Many people have experienced these symptoms for so long they consider them normal.

For exercise, the general guideline is an additional 500-1000ml per hour of moderate to vigorous activity, with more needed in hot conditions or at altitude. Electrolytes (sodium, potassium, magnesium) become important when sweating heavily for over an hour, as water alone cannot replace what is lost in sweat.

How to Use

1. Enter your body weight in your preferred unit
2. Select your typical daily activity level
3. Indicate your climate and any additional factors like exercise or pregnancy
4. View your personalised daily water intake recommendation in litres and glasses

Why This Matters

Most people are mildly dehydrated without knowing it, attributing the symptoms to tiredness, stress, or ageing. Having a clear daily water target — personalised to your body and lifestyle — gives you something concrete to aim for. Tracking your intake against this target is one of the simplest health improvements you can make, with benefits to energy, concentration, skin health, digestion, and exercise performance appearing within days.