Is “8 glasses of water per day” a myth?

Short summary

The 8 x 8 rule is not valid since water requirements vary substantially between individuals. Therefore, in order to establish a particular amount that fits all is impossible. The amount of water or fluid that this rule suggests is 1,893ml which is not based on any specific study or statistical analysis.

This rule should be treated as an easy to remember slogan not to get dehydrated in certain circumstances rather than a rule we have to obey. For a quick answer click here.

Explanation

What do we know about this rule?

1. The 8*8 rule suggests “Drinking 8 glasses of 8 ounces of water per day is beneficial for our wellness”.
2. 8 cups of 8 ounces of fluids is equivalent to 1,893ml.
3. It is not clear where this rule is originated, which results in confusion about the scientific studies it references.
4. It is also not clear whether it relates to water only or any fluids containing water (except for water contained in food) since many interpretations of this rule have circulated. It makes more sense to interpret this as 8 cups of non-alcoholic fluids rather than only water since most of the fluids contain close to 100% of water and caffeinated drinks have shown no effect on dehydration. (read more..)
5. There are many related myths which use the “8*8 rule” as a base and have attached additional claims (with no scientific backing or even disproven) onto this rule such as: “8*8 rule will help you improve your skin”, “8*8 rule will help you flush toxins from your body”, etc.
6. It has been shown scientifically that we are bound by an upper limit of how much we can drink. (read more..)
   The minimum amount varies greatly from individual to individual and depends on the amount we need to replenish the water we lose as sweat, breathing or urination.

The lack of clarity on these points surrounding this rule makes it unreliable and even misleading. If you live in a hot climate and are physically active, you will require a lot more fluid than a person who lives in a moderate climate and has a sedentary lifestyle.

Conclusion

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“8 by 8 rule” should be used as an easy to remember slogan to stay hydrated in certain situations or by people with a higher risk of dehydration, rather than a rule that we should be using as a guide on the amount of water we all need.