Eight glasses of water a day; that’s the rule.  At least that is what we’ve always been told.

Health experts have long touted eight as the magic number, but the question of how much water we really need to consume isn’t that simple.

A 100kg man who exercises a lot is quite different to a 60kg woman who works at a desk all day and that’s just one example of the many different variables that affect the glasses of water per day rule.

For example, a hot summer’s day means you might need more water, and a day of strenuous activity certainly requires more fluid. Even breast-feeding women have different hydration demands.

We can also get a lot of our fluids through food. Fruit and vegetables such as cucumber, tomatoes, watermelon and citrus can keep us hydrated. But those who might have a high salt or high fat diet need more water to get the right balance.

So what is the magic number?

While there is no single formula that fits everyone, knowing more about your body’s need for fluids and understanding the variables will help you determine how much water to drink each day.

If you want a good estimation, according to non-profit medical institute, The Mayo Clinic, adequate intake for men is roughly about 3 litres a day and for women it is 2.2 litres.

A simple rule to live by, they suggest, is to get in the habit of having a large glass of water first thing in the morning and one with each meal. Then ensure you are having at least one glass between each meal and always drink plenty of water before, during and after exercise.

Paying attention to your body’s individual needs are key because what we do know for certain is that by the time you are feeling thirsty, there is a good chance that you are, or certainly well on your way to becoming dehydrated.