A river through one life
Your body is more than half water, and it loses some all day through breath, sweat and trips to the bathroom. Topping it back up means most adults get through something like one and a half to two and a half litres of drinks every day, plus the water hidden in food. A cup here and a glass there feels like nothing, but over a lifetime it fills dozens of bathtubs and makes a real dent in a swimming pool. Each tub above holds 150 litres, about what a household bath takes, and they fill up one after another as your total grows.
Move the slider to match your usual day, counting water, tea, coffee, juice and everything else. The daily figure is compared with the official advice from the European Food Safety Authority.
How we calculate it
Children drink less than adults, so we use smaller amounts while you were young: half a litre a day in the first year (mostly milk), one litre from one to three, one and a quarter from four to eight, and one and a half from nine to thirteen. From fourteen onward we use the cups you choose, at 250 millilitres each. We multiply each amount by the days you spent at that age and add them together. Food also supplies around a fifth of the water we take in, but that is not included here.
| Who | EFSA total water advice a day | From drinks, roughly |
|---|---|---|
| Children 4 to 8 | 1.6 litres | 1.3 litres |
| Girls 9 to 13 | 1.9 litres | 1.5 litres |
| Boys 9 to 13 | 2.1 litres | 1.7 litres |
| Women | 2.0 litres | 1.6 litres |
| Men | 2.5 litres | 2.0 litres |
Worked example. A 36-year-old who drinks seven cups a day (1.75 litres) as an adult: their childhood adds about 6,300 litres, and the 22.5 years since their fourteenth birthday add about 14,400 litres. That is roughly 20,700 litres, or 138 bathtubs.
Little and often
You do not need to force down huge amounts. Thirst is a good guide for most healthy adults, and pale yellow urine usually means you are drinking enough. On hot days and when exercising, drink more, and keep in mind that older people sometimes feel thirst less strongly.
Questions people ask
How much should I drink a day?
Advice varies, but the European Food Safety Authority suggests about 2 litres of total water a day for women and 2.5 litres for men, with roughly a fifth of that usually coming from food. Needs go up with heat, exercise and pregnancy.
Do tea and coffee count?
Yes. Despite the caffeine, tea and coffee still add to your daily fluid. Most drinks count, although water is the simplest choice.
Is “eight glasses a day” a rule?
It is a handy rule of thumb rather than a scientific requirement. Eight 250 ml glasses is 2 litres, which happens to be close to official advice for many adults.
How big is the bathtub in the picture?
We use 150 litres, a typical amount for a filled household bath. An Olympic swimming pool holds about 2.5 million litres.
Sources. European Food Safety Authority, Dietary Reference Values for water (2010); Olympic pool volume from World Aquatics minimum dimensions. Calculations run in your browser; nothing you enter is sent anywhere.