Just under half of this should be in the form of drinks such as water or cold herbal teas and just under a litre from food. The remaining 300ml is created by the body from its own metabolic processes.

If you don't drink enough water, this is what happens.

1. Increase in pulse rate and in rectal temperature

2. Increase in respiration

3. Numbness and tingling are experienced in the extremities

4. Blood concentration increases

5. Lessening of the blood volume and more difficult blood circulation

The difficulty and problems of the blood circulation under such conditions leads to:

1. breathing difficulties

2. gastric upsets

3. nauseousness and loss of appetite

4. if it continues, muscular and emotional problems

In an animal study, where water was restricted the animals were highly irritable and in some cases bad tempered.

Thirst

It has been demonstrated that under intense physical activity a male will only drink voluntarily around 50% as much water as what is required to replace losses from urine and sweat. Only after rest and food do the cravings for the required amount of water return to replace the fluid deficit.

Hot Drinks

After drinking hot liquids, the internal temperature of the body rises, resulting in sweating. This cools the body down. This is sometimes used in the practice of medicine when an increase in body temperature is required for a short time, or whether sweating is required. So it is preferable to choose cool or cold drinks rather than hot ones to replace fluid losses, particularly if hot drinks are the only types of drinks that are normally chosen.

Sugary drinks

Water is the preferred choice of liquid for physical activities that last less than 90 minutes. For activities that would create fatigue after an hour or so, drinks that contain some carbohydrate are better for sustaining power output than water alone.