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The normal chemical processes within our body (metabolism) produce about a third of the total fluids we need, but what about the remainder? What we drink supplies about 60 per cent of our daily fluid intake, what we eat supplies the rest. It may surprise you to know that bread and cereals provide a source of water, and fruit and vegetables in a balanced diet can supply about 18 per cent of our needs. It is well to remember that eating plenty of soft fruit and vegetables provides water in addition to vitamins and minerals. If you are travelling and find yourself in a place where it may be difficult to get water, or where you do not trust the available drinking water, consider enjoying a freshly cut melon or a well-washed peach to quench your thirst.

It is difficult to say exactly how much water to consume because the body’s requirements vary from person to person. Our level of activity and state of health influence our needs for water, as do environmental aspects like temperature and humidity. Obviously it is sensible to increase the fluid you drink if you have perspired heavily, or if the weather is hot and dry; but by how much? The answer varies according to both vogue and scientific opinion. The middle ground seems to be between four and six glasses (1½–1¾litres/ 2½–3 pints) of water per day, with additional quantities drunk when needed to compensate for fluid lost through heavy exercise, weather and illness.

Like everything else in life, it is possible to get too much of a good thing: you actually do yourself harm by drinking too much water. Sports experts warn that some athletes – principally runners – put their health at risk in this way. Writing in the Telegraph, Peta Bee pointed out that, while hydration is important during sport, statements like ‘you cannot drink too much water’ and ‘don’t worry about the heat, just drink more’ are wrong and dangerous. Water intoxication and other problems can occur that disrupt the body’s salt balance, leading to dizziness, respiratory problems and even collapse. For those participating in strenuous exercise, such as long-distance running, a safe rule is to drink about half a glass (about a quarter of a pint) of water for every hour of exercise. Or, weigh yourself before and after exercise: replenish your fluid levels by drinking two medium glasses of water for every pound of weight lost.