Daily Water Intake Calculator

Daily Hydration Guide

Why the 8 Glasses Rule is Wrong

The '8 glasses a day' rule has no scientific basis — it was derived from a 1945 US dietary recommendation that was widely misquoted. Actual needs vary by 40–100% between individuals based on body size, activity, climate, and diet. A 50kg sedentary office worker in the UK and a 90kg construction worker in the Middle East have completely different needs.

Signs of Dehydration

Mild dehydration (1–2% of body weight) causes headache, fatigue, reduced concentration, and dark urine. By the time you feel thirsty, you're already mildly dehydrated. Practical guide: urine should be pale yellow — straw-coloured is ideal. Clear urine can indicate overhydration; dark yellow or amber means drink more.

Hydration During Exercise

Add 500–750ml per hour of moderate exercise, 750–1000ml for intense exercise in warm conditions. For endurance events over 90 minutes, plain water is insufficient — electrolytes (sodium, potassium) are needed to prevent hyponatraemia (dangerous low sodium from overdrinking). Sip regularly rather than drinking large amounts infrequently.

Food Contributes Significantly

Approximately 20% of daily fluid intake typically comes from food. Fruits and vegetables are 80–95% water by weight. A diet rich in salad, fruit, soup, and vegetables meaningfully reduces the amount you need to drink. Dry, processed-food diets increase direct drinking requirements.