Water's physiology Because of its irreplaceable role water is considered one of man's basic nutrients. Among its main physiological functions it ensures cells' total health by supplying oxygen and nourishment, increases blood flow, eliminates toxins, adjusts body temperature through perspiration, provides sufficient moisture to mucous membranes (nose, mouth and lungs), helps digestion and protects and lubricates joints.

Varying needs.  Even if we're not aware of it, every day our body loses a considerable quantity of liquids through respiration, the skin's transpiration as well as bodily functions. To compensate for these leakages the quantity of water to be reintroduced can vary appreciably, depending on individual metabolism, the climate, diet and physical activity carried out.

Water balance. At least 2 ½ litres of water a day are required for a sportsperson who works out or someone who has a very physical job in the sun. To find out how much we should drink one idea is to apply the empirical rule comparing millilitres of water to the calories in the diet. For example, if calories needed total 2,400 then 2,400 millilitres, or 2.4 litres, should be drunk. Under normal conditions however at least 1 ½ litres are recommended. Drinking a lot helps to get rid of sodium concentrates that cause water retention.

Not just water. "Pure" assumption in liquid form covers about 50% of the quantity needed; the rest comes from various drinks or foods that we eat. Broth, tea, milk and fruit juices are other sources but whole fruit and vegetables are also rich in water. Coconuts, for example, contain 95%. Care should be taken with beer and coffee though as they have a dehydrating effect and stimulate the expulsion of liquids from the body.

Thirsty hormones. The adjustment mechanism for water contained in the body is governed by the hypothalamus. By way of the anti-diuretic hormone this gland 'communicates' to the kidneys the message to withhold more of it, whilst also giving rise to a semblance of thirst.

Watch out for dehydration. During the summer or if extreme perspiration has taken place children and the elderly in particular run the risk of dehydration, or insufficient amounts of water in the body. Symptoms are headaches, sleepiness, slow reflexes, dry mucous membranes and chapped lips. Other more serious effects are weakness, hallucinations and dark urine. Dehydration can also be a problem for people who fly: due to the dry air found on planes bodily transpiration increases and can reach as high as 1.5 litres in a three hour flight!

Healthy tips. Water is enriched by other valuable mineral salts plus amino acids when it is used to cook vegetables or meat in. Vegetable broths are particularly recommended for children, are especially comforting during winter and are an excellent remedy for dehydration.

Second part. In our March article we'll learn how to identify different kinds of water, the main elements to look out for when reading labels on mineral water and the difference between the latter and water from the tap. Watch this space!