There is a very famous health tip to drink at least 8 glasses of water (or two litres) a day. But is it right? Do we really need that kind of volume of water?
Last year, a group of Australian scientists managed to prove that hydration was less important for performance than people previously believed. During exercise some athletes were given high fluid replenishment. Others were given none or very little. But they did this by rehydrating athletes intravenously, so they could not possibly know how much they were getting. The results were staggering. Hydration had no affect on performance at all.
This experiment was on the back of some marathon runners and members of the military over hydrating and getting hyponatremia - a condition where too much water reduces the amount of sodium in the body to dangerous levels.
So is the 2 litres a day rule correct?
There are too many variables to tie your consumption down to an arbitrary amount. Your body will use more water when you exercise. You will need water if you are under stress or having to think hard. If you have a nice, easy day, you are likely to use far less water. Your food has variable amounts of water in it, depending on diet.
Fruit and vegetables all have good amounts of water. Tea and coffee also have water in them, and also count towards rehydration. The climate also has significant affect on your need for water for temperature regulation. So making people stick to an arbitrary amount of water is not only impractical, but also possibly dangerous.
Funnily enough, your body has a brilliant system for measuring the levels of hydration - it's called your thirst. If you drink when thirsty, you will keep yourself in tip top health. This manic glugging of water was brought out by scientists who had proved that the body had started to dehydrate before people felt thirsty. Now recent discoveries are showing that the body can tolerate levels of dehydration without any dip in performance, and that it is very good at regulating itself through the sense of thirst.
The latest advice is to drink when you are thirsty - not out of habit or vanity.
So who really benefits from 2 litres of water consumption a day?
The bottled water companies, that's who.