Everyone knows that water is essential for life. It accounts for about 60% of our body weight and performs essential roles such as carrying nutrients and waste products and helps regulate body temperatures.

Our bodies are constantly fluctuating between different states of hydration. When our water intake matches our bodies’ requirements, this is described as optimal hydration. However, when water intake is less than our bodies’ requirements this can lead to poor hydration, usually called ‘dehydration.’

We are at greater risk of dehydration when we're either too hot or too dry, have limited access to water, or we need more water than usual. Warm or dry environments such as centrally heated homes or air-conditioned offices increase our need for our intake of fluid. We can lose additional fluid through sweating due to exercise, in hot weather climates or through illness by vomiting and/or diarrhoea.

In babies and young children, even mild dehydration can cause symptoms such as confusion, irritability and tiredness. Young children are less effective at regulating their temperatures than adults, so are less tolerant to fluid losses through vomiting or diarrhoea.

Older people are also at increased risk of dehydration. This is because the thirst sensation lessens with age and very elderly people may avoid drinking too much because of issues with continence. Persistent dehydration in the elderly can lead to confusion and even hospitalisation unless it’s dealt with promptly.

Experts recognise that a regular intake of water is vital for maintaining good health. Studies in adults show that even mild dehydration can reduce everyday mental performance, increase feelings of aggression, irritation and tiredness. Optimal hydration can even help prevent some common conditions, such as constipation, urinary tract infections, gallstones and glaucoma.

Like vitamins and minerals, our fluid requirements are individual and depend on factors such as body weight and size, physical activity and through the temperature of our environment. However, a number of different expert bodies have made recommendations for fluid and these are a good starting point.

The UK Food Standards Agency for example has based its guidance on glasses of fluid a day (i.e. over and above any fluid that we may have from foods) and adults are recommended to drink a minimum of 6 to 8 glasses a day to prevent dehydration.

Source: National Hydration Council