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Should You Really Drink 8 Glasses of Water a Day: Recommended Water Intake

Water is critical for body functions and becoming dehydrated can cause fatigue, headaches, and dry skin. We all have heard the recommended water intake for adults is eight 8-ounce glasses of water per day for proper hydration. However, do you need to drink 8 glasses of water everyday?

The short answer is: it depends. Eight 8-ounce glasses of water per day is an adequate guideline for some adults. However, in most cases how much water you should drink in a day depends on your body.

Sometimes, 8 glasses of water is not necessary. Learn about the origin of the 8x8 rule and how much water you need to drink in a day.

The 8x8 Rule

The recommended water intake for an adult is approximately 2 liters, or 8 cups, per day. This gave birth to the 8x8 rule, which recommends healthy adults to consume eight 8-ounce glasses of water everyday for proper hydration.

However in 2002, a literature review of the 8x8 rule was published in the American Journal of Physiology. The researcher, Dr. Heinz Valtin, thoroughly examined over 100 studies, peer-reviewed surveys and research articles to determine the origins of the 8x8 rule and to establish if there was any scientific proof behind it.

After examining decades of previous research, the renowned physiology professor discovered that for many of us, there is no need to drink 8 cups of water per day. He found that for healthy adults who are mildly active and living in temperate climates, they don’t need to drink such a significant amount of water.

Dr. Valtin concluded that since we also receive water from foods and other beverages, drinking 8 glasses of water may not be for everyone. Although it is important to drink water regularly, we also need to take into account the water contained in what else we consume.

Factors that Influence Recommended Water Intake

For healthy adults, our recommended water intake needed each day depends on a variety of factors.

Active level

How active we are is one of the key determinants of how much water your body needs in a day. For example, athletes who exercise regularly will need more water than someone with a sedentary lifestyle. Since your activity level can change from day to day, how much water your body needs can also change day by day.


As your body grows and changes, your recommended daily water intake also fluctuates. For instance, adults need to drink more water than children to stay hydrated. Additionally, when we become senior, we become less capable of retaining the water in our body. Thus, seniors will need to rehydrate more often than younger adultes.


Our surroundings have a huge impact on how much water we need in a day. In tropical climates, our body naturally loses more water than they would in temperate climates. When we experience hot weather, our body sweats more to maintain an optimal body temperature.

Health Conditions

What happens inside our body determines how much water we need in a day. For example, pregnant and breastfeeding women need to drink more water to provide for their babies. On the other hand, people who are sick are at higher risk for dehydration and need to drink more water to maintain proper hydration.

How Much Do We Need to Drink Each Day

Although the 8x8 rule serves as an easy to remember and simple guideline for hydration, how much water we need per day heavily depends on our own special set of circumstances. In addition, as we grow and change, our recommended water intake will fluctuate.

According to a 2004 report from the Institute of Medicine, the majority of healthy adults drink enough water each day “by letting thirst be their guide.” In addition, the report provided some hydration standards for both men and women.

Men, on average, should consume 125 ounces or 3.8 liters of total water each day, the authors wrote, while women should consume 91 ounces or 2.7 liters.

While these numbers make it seem like the majority of us don’t drink enough each day, that may not be the case. As discussed previously, foods and drinks can provide water for our body.

In other words, our diets can be a significant contributor to our daily fluid requirements. Therefore, water content beverages like coffee, tea, and milk can count towards your total water intake. Additionally, water content from common foods such as fruit and vegetables should not be neglected.

Ultimately, while the 8x8 rule can help adults with staying hydrated, most adults can prevent dehydration by letting their thirst guide them.

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