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A rough daily water-intake target from body weight, exercise, and climate.
Water (L) = weight(kg)·0.033 + (exercise min / 30)·0.35, ×climate
It starts from your body weight — about 33 millilitres of water per kilogram — then adds roughly 350 millilitres for every 30 minutes of exercise, and finally scales the total up a little in warm or hot, humid weather. The result is a rough daily fluid target in litres and ounces.
The figure is a general fluid target. In practice a fair amount of your daily water comes from food — fruit, vegetables, soups — and from drinks like tea, milk, and juice, not plain water alone. So you usually don't need to drink the entire amount as water; it is a guide to total fluid, not a glasses-of-water quota.
The cylinder fills with blue to the level of your calculated target, like a measuring jug. As you change weight, exercise, or climate, the fill rises or falls, giving an instant sense of how much each factor adds to your daily need.
Yes — drinking very large amounts in a short time can dangerously dilute the body's sodium, a condition called hyponatraemia, though it is uncommon. Thirst and the colour of your urine are good everyday guides. This calculator gives a ballpark, not a strict rule, and needs rise with illness, pregnancy, and intense endurance activity.
It is handy for planning hydration around sport or hot weather. A 70 kg person doing 30 minutes of exercise in a temperate climate lands near 2.7 litres; the same person on a hot, humid day a bit higher. Athletes, hikers, and people working outdoors use estimates like this as a starting point and then adjust to how they actually feel.