Two litres a day is not a number that fits everyone. What actually decides how much you need.
The two-litre rule is widely repeated, but there is no reason a person weighing 50kg and one weighing 90kg, or a desk day and a summer run, would need the same amount. Guidance generally scales with body weight and activity, and rises with heat and sweat. Knowing your own baseline is more useful than memorising a single figure.
A large share of daily fluid comes from food. Soups and stews, fruit, vegetables and milk all carry a lot of water, and coffee and tea add fluid on balance even after their diuretic effect. If your meals include soup often, you may reach enough without drinking much water separately.
The simplest signal is urine colour. Pale yellow usually means you are fine; consistently dark means you are behind. Thirst arrives only after you are already short, so relying on thirst alone is late. Thirst also fades with age, which is why drinking on a schedule is safer for older adults.
Drinking a very large volume in a short time can dilute the sodium in your blood enough to cause harm. It is rare but real, and it shows up mainly when people drink only water during long exercise. For prolonged sweating, replace salt along with fluid.
Attaching drinking to something you already do lasts longer than trying to hit a target. Keep a cup in sight, take one with each meal, take a sip whenever you stand up. If you have kidney disease or a fluid restriction, general advice does not apply to you as written.
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