Water

Around 60 per cent of an adult's body weight is water. It must be continually replaced since we lose roughly 0.3 litres of water a day simply through breathing. In a lifetime, each person is estimated to drink about 40,000 litres of water.

We need water for digestion and the elimination of waste products. It acts as a lubricant for joints and eyes, and is essential for the regulation of body temperature. Both drink and food supply water. The total intake from drinks - including tea, coffee or juices - plus around 300ml of water which is obtained as a byproduct of metabolism, provides roughly 2 litres a day, while food - especially fruit and vegetables - supplies a further litre. This makes a total of around 3 litres of water each day for the average adult.

When you take any form of vigorous exercise or when the weather is particularly hot, you should always drink more than normal, to compensate for the extra water lost through breathing rapidly and sweating. By drinking plenty of water you can ensure that calcium in the urine is diluted - in high concentrations, calcium can crystallise and form kidney stones. Water flushes out bladder and kidney infections and improves the complexion by washing out the body's waste products.

People who drink too little water may suffer from Headaches and poor concentration. But surprisingly, it is possible - although difficult - to drink too much water. If a lot of water is taken in a very short space of time, it can cause short-lived symptoms which are similar to those of being drunk.

Water filters

Many people use water filters to remove minute traces of chemicals, metals and other substances that may be present in tap water. Whatever filter system you choose, you must replace the filter regularly, according to the manufacturer's instructions. If the filter is overused, it will start to release pollutants back into the water and breed bacteria.

There are three main types of filter. Activated carbon filters include the type in which you pour tap water through a filter which sits on top of a jug; they remove chlorine, pesticides and some chemicals, but not fluoride or nitrates. Distillation units remove most impurities through a process in which the water is vaporised then condensed. However, many people find the taste of distilled water rather bland, and the distillation units use a lot of electricity. Reverse osmosis systems force filtered water through a membrane; they remove virtually all chemicals and minerals, including those such as calcium and magnesium which benefit health and enhance the flavour of drinking water. Once water has been filtered in this way it should be used immediately or refrigerated and used within 24 hours.