The human body is about two-thirds (approximately 70%) water. Water is essential to the normal working of your body. It lubricates the joints and eyes, aids digestion, flushes out waste and toxins and keeps skin healthy.

Dehydration occurs when the normal water content of your body is reduced. This leads to a change in the vital balance of chemical substances in your body, especially sodium (salt) and potassium. In order to function properly, many of the body’s cells depend on these substances being maintained at the correct levels.

Even though your body is mainly made up of water, the amount of water in your body only has to decrease by a few per cent, for dehydration to occur. The effects of dehydration can be serious and, in extreme circumstances, they can be fatal.

You can avoid becoming dehydrated by drinking plenty of water. It is recommended that you should drink 1 to 2 liters (6 to 8 glasses) of water every day. If you are active, or if the weather is particularly hot, there is a greater risk that you will become dehydrated. To prevent dehydrating, you should increase your fluid intake. You should also increase your fluid intake if you are ill with sickness and/or diarrhea.

When exercising, you should drink up to one liter of water per hour of exercise, on top of your normal daily amount. This should be increased if you are exercising in warm conditions, as you will sweat more and fluid will be lost from your body more rapidly. You should always ensure that you are drinking enough water to replace lost fluids.

In rare cases, it is possible to over-hydrate while exercising. This condition, known as hyponatremia, is low sodium, and can occur when too much water is drunk in a very short time. The condition sometimes affects endurance athletes whose blood sodium is reduced through sweat and then further diluted by drinking large amounts of water. Typical symptoms of hyponatremia include; nausea, vomiting and headache. In the most serious cases, the brain swells causing confusion, seizures, coma and even death.