Most of us already know that the body can survive without food for weeks, but cannot survive without water for more than a few days. Water accounts for about two thirds of our body weight and is vital for normal cellular functioning, therefore it is extremely important to maintain an adequate supply of water in our bodies. Most people stay adequately hydrated in day to day life, but when physical stress (such as exercise) is placed upon the body the need for water increases, and therefore the chances of dehydration increases. So it is important to "top up" your fluid intake when you are exercising. Water is a nutrient (along with Vitamins, minerals, fats, carbohydrates, proteins).
Adults are recommended to drink around 8 glasses of water (from a 250ml glass) per day (so around 2 litres). This usually includes tea, coffee, and even alcohol. Although these products can dehydrate you, the water they do contain can in fact hydrate you. The amount you require will depend on your age, activity level, and even geography (due to humidity). Most of the liquid we drink accounts for the two thirds of the water necessary for survival, this means we need another litre from somewhere for our bodies to function normally. We get that extra litre from food. Most of this water comes from fruits and vegetables, as well as dairy products, and in smaller quantity's cereals, breads, and meat products. So in all the average requirement of water for our bodies is around 3 litres.
Some interesting facts about water:
Is Calorie free.
It transports blood.
Passes other nutrients through the cell membranes in our bodies.
Water carries the waste that is excreted from the body
Water accounts for between 50-70% of our total body weight.
The absolute minimal intake of a non-active person is 1.8L per day (including food).
Losing one fifth of the body's water can be fatal.
The body can produce its own supply of water, (though this is minimal)- via cellular respiration.
Body temperature is regulated by water.
Water and exercise
To stay alive we need water for our cells, as water helps our bodies to make energy. When we exercise, we need more energy, and because we need more energy, we need more water. Because your activity level has increased, so has the activity of the billions of cells in your body (your cells are trying to supply your body with energy). This process is called cellular respiration.
This is why your body temperature increases when you exercise, because everything in your body is going at a faster rate. The human body's temperature needs to remain at a constant level (around 36.5C). So when you exercise your body needs to keep its temperature down, this is why we sweat. Sweat reduces the body's temperature by evaporation.
When the body is moist from sweat, evaporation of that sweat naturally occurs. This evaporation cools the body by removing heat from the body. This is why it is extremely important to keep hydrated during exercise. Recommended intake of water during exercise is; 2 cups (250mls) of water before commencing exercise (over a period of 2hours). Then 1 full cup every 15-20 minutes whilst exercising. This will avoid dehydration.
Signs & Symptoms of Dehydration
Fatigue headache, poor concentration, very (yellow) urine, nausea, dizziness, and finally exhaustion and disorientation. This should never happen if you are sensible about exercising and hydration. However if the temperature is above 32C, or the humidity more than 40%, sweating does not reduce heat effectively, and heat stroke can occur. So try and avoid if possible exercising in these circumstances.