Written by Denise Dahdah, NetDoctor journalist
In recent years, drinking large quantities of water has become one of the mantras for healthy living. Every magazine has had its version of 'drink water and be healthy' or 'drink water and lose weight'.
But do we really need to drink the mythical eight glasses of water every day?
Doctors advise that we should drink at least 1.2 litres (2.5 pints) of water a day.
Human beings are made up of around 75 per cent water. Two thirds of our bodily water is found inside our cells, with the rest between the cells and in our blood.Water provides the medium in which all the body's chemical reactions take place and the solution in which foodstuffs are dissolved and transported. It helps regulate our body temperature through sweating.
A 2 per cent loss in the water surrounding our cells can result in a 20 per cent drop in energy levels. That's how important water is for us.Water is the most vital requirement for human life. While our bodies can survive without food for around three weeks, without water we can only live for three days.
Dr Keith Barnard, GP, says: 'The body tries desperately hard to retain water if there is no intake, so hardly any urine is passed. If a person is in a normal temperature and not exposed to the wind they could probably last longer than three days - maybe as long as a week.
'We cannot live long without water because we have no reserves of it in our body. So do you really need to drink at least eight glasses of water every day?
On average, your body loses 1-1.5 litres of water a day. If someone is undertaking a lot of activity, and therefore breathing and sweating more, they would lose more.
Dr Barnard says: 'It is not essential to always drink a set amount regardless of circumstances. The body is very good at regulating water. 'If you drink too much, your body will get rid of the excess, so you will pass urine more often and it will look almost clear. 'If you don't drink enough, your body will save water by concentrating your urine, which will look darker, and your brain will tell you that you need more water by making you feel thirsty.'
Another thing to keep in mind is that water is found in fruits, vegetables, milk and juices. Water from these sources will go some way to meeting your daily requirements, so people do not need to drink a full eight glasses of water on top of this (see Table 1).
Senior nutrition scientist Gail Goldberg says: 'There is a perception generated, for example by newspapers and magazine articles, that all our water requirement has to come from "water". 'My colleagues and I would never say that people should only drink water. It's a matter of individual choice and availability.'
The Macrobiotic Association of Great Britain (MAGB) says that a person following a macrobiotic diet does not necessarily need to drink as much water as someone who is on a regular diet.
Macrobiotic cook and teacher Bob Lloyd says: 'The type of foods we [people following a macrobiotic diet] eat contain a lot of water and are less dehydrating, therefore there is less need to drink.
'Can drinking water help you lose weight?
A reasonable water intake can help with weight loss. We need around half a cup of water for every 100 calories we burn.
Dr Roger Henderson, GP, explains: 'Drinking before eating may help you lose weight because the brain can generate energy from water and food. 'When water is used instead of food then none is stored as fat - as is the case with unused food - and excess water passes out of the body with no weight gain.
'Drinking before food helps to fill the stomach and increases the chance of weight loss by making the person eat less.'
So how much should you drink?
The minimum figures for the body's daily water loss are 500ml through urine and 700ml through breathing and sweating.
Doctors advise that to be on the safe side we should drink at least 1.2 litres of liquids (2.5 pints).
So, remember, although water is essential, you don't need to become obsessed about drinking eight glasses a day!