Water is one of the most important nutrients the body needs. It makes up 60-70% of our body and is essential for all cells, organs and systems to work properly. Some of the vital functions of water are the following:

  • Water provides the transportation system of the body (it moves nutrients, oxygen, vitamins and minerals to where they are needed) and helps to take waste products away.
  • It helps to regulate body temperature.
  • Water is the environment in which every single chemical reaction in our body takes place. The water content of each individual cell and the whole body needs to be kept constant between very narrow limits, so that metabolism and all other body functions (i.e., digestion) remain efficient.


How much water do we need?

The amount of water and other fluids that we need to drink each day varies from person to person, depending on age, time of year, climatic conditions, diet and the amount of physical activity we do. Water requirements are particularly increased in hot climate and when physically active.

It is estimated that an average sedentary adult should drink 1-2 litres of water per day. Activity, even walking, will increase water loss. An hour of exercise could be responsible for a further 1-2 litres of water loss, depending on intensity and weather conditions (the higher the intensity and the warmer the climate, the bigger will be fluid loss).


Sources of water in diet.

Some water intake will come from the food eaten. It has been estimated that roughly 20% of water consumed daily is from food. Fruit and vegetables, for example, have very high water content in addition to other nutrients. Remaining 80% of water should come from beverages, and the best way to get enough water every day is to drink water itself.


Is it possible to drink too much water?

Although very uncommon, it is possible to drink too much water. The result is a condition called hyponatremia. Drinking a high volume of water over a short period of time (before the kidneys have time to filter out the excess) means the sodium concentration in the blood can become very low. In this instance the following symptoms may occur: headache, confusion, muscle spasms, weakness and nausea. In very severe cases, water can enter the cells causing them to swell. Most cells can cope with some degree of swelling, but if it happens in the brain cells, this can be fatal.

It is preferable to consume water little and often throughout the day.


Consequences of dehydration.

The consequences of not having enough fluid can be serious. Fluid loss is measured as a percentage of body weight.

For example, if an 80kg person is 2% dehydrated, it means he has lost 80*2% = 1.6kg of water (1 litre of water weighs approximately 1kg).

A loss of 3%of body fluids results in a reduction in blood volume and blood flow, inefficient kidney function, a measurable reduction in exercise performance, and symptoms such as dry mouth and headache.

At a 4% loss, the capacity for hard muscular work declines by 20-30%.

At 5% loss, heat exhaustion will result, requiring medical attention.

At 7% loss physical and mental functions become severely affected and the individual can begin to hallucinate.

At 10% loss, dehydration can lead to heat stroke, circulatory collapse and death.



A diuretic is a substance that encourages water loss from the body. The most common examples are drinks containing caffeine (coffee, tea, cola, etc.) and drinks containing alcohol.


Caffeine is a stimulant, affecting central nervous system. It can increase endurance, concentration and mental alerting. However, it also stimulates kidneys to excrete more water than they otherwise would. Hence, too much caffeine can lead to dehydration. But it does depend on how much fluid is taken in along with the caffeine. For example, a large cup of relatively weak coffee (i.e., lots of water) could actually result in a net fluid gain, whereas a small cup of extra strong espresso (very little water) would lead to a net fluid loss.


Alcohol is also a diuretic. Many of the symtoms of a hangover (headache, dry mouth, nausea) are purely symptoms of dehydration. Drinking water and soft drinks mixers along with alcohol will help to replace some of the lost fluid.

Anastasia P., Sources: British Nutrition Foundation, UK Health Department