Eight glasses is the answer everyone knows and nobody can source. The real guidelines are both higher and more flexible than that, and there is a check you can run in the bathroom that beats any target on a chart.
The European Food Safety Authority puts adequate total water intake at about 2.0 litres a day for women and 2.5 litres for men. US guidance is higher still — roughly 2.7 and 3.7 litres. The crucial word in all of them is total. That figure includes the water in your food, which is typically 20–30% of the total. Fruit, vegetables, soup, yoghurt and even bread all carry water. So the amount you need to actually drink is closer to 1.5–2 litres for women and 2–2.5 for men — and tea, coffee, milk and squash all count toward it.
Look at the colour of your urine. Pale straw or light yellow means you are well hydrated. Consistently dark yellow or amber means drink more. Completely clear, all day, usually means you are drinking more than you need — which is not dangerous for most people, just unnecessary. Thirst is also a better signal than it gets credit for. Healthy adults have a well-calibrated thirst mechanism; the main exceptions are older adults, whose thirst response blunts with age, and anyone in the middle of hard exercise or heat, where losses outrun the signal.
- Exercise: add roughly 400–800 ml per hour of training, more in heat. If a session is longer than about 90 minutes or you sweat heavily, include some electrolytes rather than plain water alone. - Hot weather: sweat losses can double or triple, and they climb before you feel thirsty. - Illness with fever, vomiting or diarrhoea: fluid and salt losses both go up. - Pregnancy and breastfeeding: guidance adds roughly 300 ml and 700 ml a day respectively. - High altitude and dry air, including a long flight: you lose more through breathing than you notice.
Mild dehydration is easy to misread as hunger, and it shows up as exactly the vague low-energy afternoon that sends people to the biscuit tin. Logging water alongside meals is not busywork — it is the cheapest explanation to rule out when you are trying to work out why 15:00 is always difficult. It is also the easiest habit in the whole tracker to build, which makes it a good first streak. One tap, several times a day, no measuring and no decisions.
Nobody drinks more water because a chart told them to. They drink more because a full glass is within reach. - Anchor it to things you already do: a glass when you wake up, one with each meal, one when you sit down at your desk. - Keep a bottle you like in the place you actually sit. Visible beats virtuous. - If plain water bores you, add lemon, mint or cucumber — flavoured or sparkling water hydrates exactly as well. - Watch caffeine late in the day for sleep reasons, not hydration ones. Coffee and tea are net hydrating at normal intakes.
Put it into practice today
CoreFeed turns the logging into a daily quest — log a meal, feed your Anima, keep the streak.
Start tracking — freeYes. The idea that caffeine dehydrates you does not hold at normal intakes — the water in the cup more than offsets the mild diuretic effect. Three or four coffees a day count toward your total.
Rarely, but yes. Drinking very large volumes very quickly can dilute blood sodium (hyponatraemia), which is a genuine medical emergency. It mostly happens in endurance events. Normal drinking spread across a day is not a risk.
Most likely a misread of a 1945 US Food and Nutrition Board recommendation, which suggested about 2.5 litres a day and then noted — in a sentence that got dropped — that most of it comes from food. The number survived; the caveat did not.
Indirectly. Water has no calories, so replacing sugary drinks with it removes calories outright, and a glass before a meal modestly increases fullness for some people. It is a useful habit, not a mechanism.