If you are feeling drained and your energy levels seem to be at an all time low, ask yourself this; how much are you drinking?

Dr Susan Shirreffs, an expert on dehydration from the Biomedical Sciences Department at Aberdeen University, says, "Most people probably need to drink between one and two litres of fluid every day to maintain their health. Even small levels of dehydration can create headaches, lethargy, or just overall lack of alertness."

The situation can become serious. People who regularly drink very little are at long term risk for problems with their kidneys, mental functioning, digestive system and even their heart. This is perhaps not so surprising when you consider that the amount of blood that you have circulating in your body reflects the amount of water you drink.

If you reduce your fluid intake, the volume of blood goes down and there is less available to flow to the heart, brain, muscles and all the important organs. The less blood delivered to these crucial organs, the less oxygen they receive and the less able they are to perform their normal tasks.

Knowing When To Drink

Unfortunately you cannot rely on your thirst mechanisms to tell you when it is time to take a drink. By the time you register feeling thirsty, you are already slightly dehydrated. The key is to keep topping up with liquids throughout the day.

-- Children It is especially important to keep on eye on how much and how often children drink. Their sense of thirst is not as well developed as in adults. In addition, as they are often dashing around and physically active, it is important to regularly offer them water and hot and cold drinks to maintain a good fluid balance. This is particularly so in the hotter summer months when, like adults, their bodies also lose water through perspiration trying to keep cool.

-- Older People Just as young children's thirst mechanisms have not fully matured, as we age, these mechanisms are beginning to get less sensitive with age. Combine this with the fact that many older people deliberately restrict their fluid intake to avoid the need for regular and often physically exhausting trips to the toilet, there is an increased risk of dehydration. For the elderly, regular intake of their favourite fruit juices and water, tea, coffee, hot chocolate and soups are recommended throughout the day in addition to water.

Getting Active

Exercise is thirsty work! You not only lose fluid through sweating, again, the body's way of cooling you down, but also as water vapour in the air that you breathe out. The harder and longer you exercise, and the hotter and more humid the place where you are exercising, the more fluid you will lose. The levels of loss can be surprisingly high and if fluid is not replaced quickly, dehydration will follow, significantly affecting physical performance. For accurate fluid replacement it is advisable to weigh yourself before and after exercise and to drink a litre of fluid for every 1kg of weight loss. Otherwise, drink a litre of water per hour of hard exercise.

The best advice is to drink before, during and after exercise. Either water or isotonic drinks in which the mineral salts and glucose are equal to those in the blood are the best options.

While fluids are essential, don't forget to keep an eye on your calorie intake from drinks. Try to balance your choices of drinks to correspond to your energy output.

And remember, keeping up your fluids is not just about feeling well and optimising your health on the inside. Having sufficient fluids is also a great beauty aid; it helps keep your skin hydrated and healthy looking from the inside out.