The advice to drink eight glasses of water daily has persisted for decades despite lacking strong scientific backing. Hydration needs vary with body size, climate, activity level, diet, and health status. A 90 kg athlete in humid heat requires far more fluid than a 55 kg office worker in air conditioning.
How Much Do You Actually Need?
A practical starting point is 30–35 ml per kilogram of body weight daily, plus additional fluid for exercise and heat exposure. Roughly 20% of daily water intake comes from food — fruits, vegetables, soups, and yogurt all contribute. Coffee and tea count too, despite old myths about their diuretic effects at normal consumption levels.
Our water intake calculator estimates a personalized target based on weight and activity minutes. Treat the result as a guide, not a prescription.
Reading Your Body's Signals
Urine color is the simplest hydration check: pale straw indicates adequate intake; dark amber suggests you need more fluid. Thirst is a late signal — by the time you feel thirsty, you may already be 1–2% dehydrated. Headaches, fatigue, and reduced concentration often precede obvious thirst.
Overhydration (hyponatremia) is rare but possible during extreme endurance events when sodium is lost faster than replaced. For most people, the risk is under-drinking, not over-drinking.
Electrolytes Matter
Water alone does not replace sodium, potassium, and magnesium lost through sweat. Sessions exceeding 60 minutes in heat benefit from electrolyte supplementation. Whole foods — bananas, leafy greens, nuts — provide these minerals without processed sports drinks.
Hydration Habits That Stick
Keep a visible water bottle at your desk. Drink a glass upon waking and before each meal. Set hourly reminders if you forget. Flavoring water with lemon or cucumber makes it more appealing without adding significant calories or sugar.