How much water do you actually need?
The "8 glasses a day" rule has almost no scientific basis — it came from a 1945 US dietary recommendation that included fluid from food, and somehow lost that context along the way. Actual needs depend on body weight, activity level, climate, and diet. Heavier, more active people in hot climates need significantly more.
The 33 ml/kg baseline this calculator uses is a reasonable starting estimate. For a deeper look: Daily Water Intake — The Real Answer.
FAQs
Does coffee count toward my daily water intake?
Yes. Despite caffeine's mild diuretic effect, research consistently shows that regular coffee drinkers don't end up more dehydrated — the fluid in the drink offsets the effect. Tea counts too.
How do I know if I'm drinking enough?
Look at your urine colour. Pale yellow (like weak lemonade) means you're well hydrated. Dark yellow or amber means drink more. Completely clear can actually mean you're overdoing it.
How much extra should I drink when exercising?
Roughly 400–600 ml per hour of moderate exercise. Thirst is a fairly reliable guide once you're not chronically dehydrated.