Usually about two and a half litres of water is needed each day for a reasonably sedentary adult to replace the total water loss that occurs through skin, lungs, faeces and urine, unless they are in an unusual environment.

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. The pulse rate goes up and there is an increase in the rectal temperature

2. Respiration rate goes up

3. Numbness and tingling are experienced in the extremities

4. Increase in concentration of the blood

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

The difficulty and inadequacy of the circulation of blood under these conditions leads to:

1. breathing problems

2. gastrointestinal upsets

3. nauseousness and loss of appetite

4. if it carries on for an extended period it will cause problems with muscle movement and unstable emotions

In a scientific study involving animals, the restriction of water gave rise to irritabliity and for some, bad temper.

Thirst

It has been shown that under intense activity a man will voluntarily drink only about half as much water as what is needed to replace his losses from sweating and urine. Only after food and rest does a person crave the water needed to replace the 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.

Sugar 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.