How much water should you drink a day?

A common guideline is about 30–35 ml of water per kilogram of body weight per day, adjusted up for exercise and hot weather. For many adults that lands between 2 and 3 liters (roughly 8–12 cups) of total fluid per day.

Yes. In normal amounts the fluid in coffee and tea contributes to your daily hydration. Very high caffeine intake has a mild diuretic effect, so plain water is still the best base.

It starts from about 33 ml per kilogram of your body weight, then adds an allowance for your activity level and for hot climates to estimate your total daily water target.

No — plain water has zero calories, whether it comes from the tap, a bottle, or a filter, because it contains no carbohydrates, protein, or fat. Only flavored, sweetened, or "enhanced" waters add calories (often 50–120 per bottle), so plain water is the easy choice when you're watching your intake.

Plain water doesn't spoil, and there's no official shelf life for bottled water. Manufacturers still print a date — usually around two years — mainly for best taste, since flavor and the plastic bottle can change over time. Kept sealed, cool, and away from sunlight and strong smells, water stays fine to drink.

For most people the best choice is simply clean, plain water — tap water where it's safe and regulated, or filtered water. Both tap and bottled water also provide helpful minerals like calcium, magnesium, and potassium. What matters most is drinking enough consistently and choosing water over sugary drinks.