Water Intake Calculator

The base recommendation is about 35 ml per kg of body weight per day for a sedentary adult in a temperate climate. For a 70 kg person, that's around 2.45 L/day. Active people and those in hot climates need significantly more. Use the calculator above for your specific target rather than relying on the oversimplified "8 glasses a day" rule.

Yes - larger bodies have more cells and metabolic processes requiring water. The base formula is 35 ml per kg at rest. A 50 kg person needs roughly 1.75 L/day; a 100 kg person needs about 3.5 L before activity or climate adjustments. This is why generic recommendations aren't accurate for everyone.

Exercise increases water loss through sweat and respiration. A moderate workout can cause 0.5–1 L of extra fluid loss. Intense daily training can add 1–2 L. The ACSM recommends 500–600 ml before exercise, 200–300 ml every 15–20 minutes during, and replacing 150% of any weight lost afterward. This calculator adds 500 ml for active and 1,000 ml for very active lifestyles.

All beverages count - water, herbal tea, coffee, milk, and sparkling water. Food also contributes: fruits and vegetables are 80–95% water and can account for 20–30% of daily fluid intake. However, plain water remains the most efficient source with no calories, sugar, or diuretic effects.

Yes - excessive water intake can cause hyponatremia (dangerously low blood sodium). This is rare in daily life but can occur during endurance events when athletes drink large amounts of plain water without replacing electrolytes. For most people, the kidneys can process up to 0.8–1 L per hour, so drinking beyond that rate is the main risk to avoid.

Absolutely. In hot or humid conditions, your body sweats more to regulate temperature, significantly increasing water loss. Moving from a temperate climate to a hot one can increase daily fluid needs by 500–1,000 ml. High altitude also increases respiratory water loss. This calculator adds 500 ml for hot or humid environments.

Early signs include thirst, dry mouth, darker urine (aim for pale yellow), and mild fatigue. Even 1–2% fluid loss can cause headache, dizziness, and difficulty concentrating. Severe dehydration (5%+) is a medical emergency. A practical rule: if your urine is darker than pale yellow, drink a glass of water now.

Yes. AI health apps like Lemon Health send smart hydration reminders based on your schedule and activity - not just generic alerts. Lemon learns when you tend to skip drinking and nudges you at exactly the right moments. Building a consistent hydration habit is one of the simplest, highest-return health actions you can take.