Myth vs. Fact: do you really need eight glasses of water a day?

Every Wednesday we take one thing almost everybody believes and check it.

The myth: everyone needs exactly eight glasses of water a day.

The fact: there is no single number that fits everyone, and plain water isn't the only thing that counts.

How much fluid you need depends on your size, how active you are, the weather and your health. A tall person doing yard work on a hot day needs a lot more than someone sitting at a desk in winter.

Water also comes from more places than the glass. Milk, tea, coffee, soup, and foods such as fruit and vegetables all add to your total. Many people get a good share of what they need from food alone.

So where did the eight glasses come from? Nobody is fully sure. It may come from an old recommendation that counted water from food too, which got lost as the advice was repeated.

What to do instead: drink when you're thirsty, drink more when it's hot or you're active, and keep an eye on the colour of your urine. Pale yellow is generally a good sign. If you have a health condition, ask your doctor what's right for you.

Small, simple habits matter more than a perfect number. That goes for sleep too: the cheapest health upgrade.