It is known that about 60% of our body is made up of water. Water is an essential nutrient for almost all forms of life. We all know that it is very important for various functions of the body. It helps in regulating body temperature, digestion and distribution of nutrients, removing waste products from the body, blood circulation, keeps the tissues moist etc.
It has been understood that as the body loses water, different functions are affected. At just 1 % loss, thermoregulation is impaired, and as water losses increase, thirst increases and then progressively, dry mouth, discomfort, loss of appetite, decrease in work capacity and therefore productivity. In higher water losses of about 6% there is numbness and tingling sensation in body extremities such as finger tips, toes. Higher losses can lead to a person collapsing and can sometimes be life threatening.( http://www.who.int/water_sanitation_health/dwq/nutwaterrequir.pdf )
So, the most important question which everybody wants to know, is how much water should one have. The answer to that is, there is no specific amount. There is no RDA (Recommended Dietary Allowance) for water. This is because every person has a different weight, dietary practices, lifestyle, age. There is a common practice of recommending 8 glasses of an 8 ounce glass, also known as 8x8 rule. That is, 8 glasses of a glass with a capacity of about 237 ml. But how did this practice start?
In an article by Heinz Valtin in the American Journal of physiology ( "Drink at least 8 glasses of water a day." Really? Is there scientific evidence for "8x8"? November 1, 2002 Vol 283 no. 5, R 993-R 1004) it has been mentioned that this might have its origin from 1945 when the Food and Nutrition Board of the National Research Council wrote:
A suitable allowance of water for adults is 2.5 liters daily in most instances. An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods.
Which means, apart from the water which is consumed, food also provides a certain amount of water. But there is no study which states that one should have 8 glasses of water. Therefore, many believe that one need not drink that much water.
But the basic point about water consumption is, it is not the same for everyone. A lot depends upon the environmental conditions, activity level of the individual and the body weight. If one wants to be specific, there are daily water intake calculators online which take under consideration all these factors.
In a country like India where the summers are very harsh, one must drink a lot of water. I have come across people who drink as much as 4 liters of water because of extreme climatic conditions.
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Although there is no study to back the 8x8 rule or 8-10 glasses rule, it is not a bad practice. As I mentioned, with the kind of climate that we face in our country (except the winter months when water requirements would be less), can we afford to have less water than this? I would think not. If one cannot bring themselves to drink as much, start with just half a glass at a time and gradually increase the amount. As mentioned above, by the time one feels thirst, the body has already lost 1%. So many experts believe waiting to feel thirsty is not a good way of judging water requirements.
Water toxicity is a condition which happens if a person has too much water in a short amount of time. According to American Chemistry Society, it takes about 6 liters of water to kill a 165 pounds (75 kg) human being.
This condition mostly occurs in endurance sports when an athlete consumes too much water while running, water drinking contests or if a person is involved in activities which causes heavy sweating and to replenish that ends up consuming too much water in a short span of time.
Too much water causes a drop in sodium levels leading to something called hyponatremia.
Under normal circumstances, a person would rarely have water toxicity. So, drinking 8-10 glasses for a moderately active person will be beneficial. For anyone who wants a specific amount try the water intake calculators online. Below is a link to one of the online sites.