How Much Water Should We Really Be Drinking Per Day?

2011-07-07 | |
Last updated: 2019-10-04

Aside from air, water is the most fundamental requirement for sustaining human health and life. It is well known that within days, dehydration can kill. In the hot summer months, public officials and the media constantly encourage us to “drink plenty of water”, about 8 glasses per day. At the same time health publishers are constantly reminding us of our need to be well hydrated.

Sports_Bottles_topWhile we continually receive this barrage of messages about the dangers of dehydration and the need to consume glass after glass, we are almost never provided a suitable explanation. At the same time, the idea of drinking 8 glasses of water daily brings to mind little more than a long series of restroom breaks for many of us. Obviously, there is a disconnect between what we are being told and what we observe so it is important to understand the health benefits that water actually provides.

Should We Be Drinking 8 glasses Of Water Daily?

The idea that we should be drinking 8 glasses of water daily can be found everywhere. This makes it difficult to determine where the idea originated. However, a researcher from Dartmouth Medical School believes that the number may be the result of a misinterpreted recommendation from the US National Research Council’s Food and Nutrition Board.

The organization does indicate that individuals should consume up to 2.5 quarts or 2.4 liters of water daily. However, the Food and Nutrition Board also indicates that much of this water comes from the food we eat. This detail was likely missed and the resulting volume of water was probably divided up into the standard portions that people would normally consume. The result of this omission is the “recommendation” to drink 8 glasses of water each day.

Now, this is not the only myth associated with drinking water. Beverages such as tea, coffee and sodas are frequently excluded in the daily water total because the sugars and caffeine contained in them pull water from our bodies. However, even with the caffeine and sugar, the amount of water entering our bodies when drinking these beverages is greater than the amount of water we lose. Our bodies don’t get as much benefit as when we drink water, but there is still certainly a benefit.

The last myth to cover here that is associated with drinking water is the idea that the feeling of thirst comes slowly. This implies that we are already dehydrated by the time we feel thirsty. However, biological science has found that a healthy person will feel thirst when the concentration of their blood increases by only 2%. Dehydration, in contrast, is defined medically as the blood concentration being increased by 5%. Clearly, there is some room to recover fluids after the feeling of thirst.

To give an idea as to how much water this is, a typical adult body holds 40 liters or 42 quarts of water. This means that to go from a feeling of thirst to the point of dehydration, we would have to lose another 5 typical glasses of water. It also means that we only have to drink two medium bottles of water to be fully hydrated.

Taking all of this into consideration, drinking 8 glasses of water each day is probably too much for the average person. However in some cases, increased water consumption makes sense. More than anything, its important to drink enough water to avoid the health effects of dehydration.

What Are The Benefits Of Water To Our Health?

Putting aside all the health information about water that is really tied to dehydration, the health benefits of additional water are actually few. However, these benefits affect enough of us that it is important we know what they are.

Managing Low Blood Pressure

While high blood pressure receives considerable attention because it is so common, there are people who suffer from low blood pressure. For those with such conditions, fainting is a problem. For these individuals, increasing blood pressure is possible by drinking additional water. Research from Imperial College London found that drinking only 2 glasses of water was enough to prevent fainting and weakness by raising blood pressure.

Cancer Prevention

Another of the benefits of drinking additional water that has some merit is in the prevention of certain types of cancer. In research from Fred Hutchinson Cancer Research Center, the risks of colon cancer were found to be lower when daily consumption of water was higher. Specifically, the research found that women who drank 5 or more glasses of water daily had a 45% lower risk of colon cancer than women who only drank 2 or fewer glasses. For men, 4 or more glasses of water consumed each day reduced the risk by 32% over men who drank less than a glass per day.

It is important to note that these results came from only drinking about half of the 8 glasses that are frequently recommended.

Another form of cancer prevention that benefits from additional water consumption is for bladder cancer. Research from Harvard University found that the risk of bladder cancer was reduced by roughly 50% when individuals consumed the equivalent of 6 glasses of water per day in comparison to those who only consumed 1 glass. Again, these reductions in risk were observed without explicitly drinking 8 glasses of water daily.

One last form of cancer prevention that benefits from additional water consumption is for breast cancer. A small research study from the University of Sheffield found that the risk of breast cancer was reduced by almost 70% for women who reported drinking any amount of water as compared to women who only drank other beverages. While the study is certainly incomplete, it does highlight the benefits of water drinking and shows that the benefits are experienced without drinking large amounts of water.

Maintaining A Healthy Weight

Aside from cancer, additional water consumption can have health benefits in terms of weight management. Research from Virginia Tech found last year that drinking two cups of water at the start of each meal reduced calorie consumption by 75 to 90 calories. This approach can also help those on moderate diets lose roughly 40% more weight over a 3-month period. Given the increasing numbers of overweight individuals, these findings offer an important approach to improving health.

Reducing Diabetes Risk

One last benefit of drinking more water is with respect to high blood sugar and subsequently the risk for developing Type 2 Diabetes. A recently released research study from Emory University found that people who drank 4 glasses of water per day had a 21% lower risk for developing high blood sugar over the next decade when compared to who those who drank less water. Although this was early research, it is still promising. Again in this case, the benefits were seen with only half the water that is too often recommended.


Although water consumption is heavily promoted, we are rarely offered accurate information regarding the benefits that it provides. At the same time, we are told to drink more than most people would find reasonable. Much of the information we receive about water’s health benefits is actually about dehydration. That is unfortunate because additional water consumption does have clear benefits although far fewer than we are often led to believe.

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Category: Disease Prevention, General Health

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