Written by Hrefna Palsdottir, ms — median reviewed by Kim Chin, RD, Nutrition — updated on October 12, 2021

You’ve most likely heard the you must drink eight 8-ounce (240-ml) glasses of water every day. That’s half a gallon of water (about 2 liters).

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This claim has become widely accepted as fact, and also it’s really easy to remember. Yet is there fact to this advice, or is it simply a myth?

This article reviews the evidence behind the “eight glasses a day” rule and how lot water we need each day.

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It’s tough to pinpoint specifically where and also when the “eight glasses every day” dominance originated. There room theories the it may be based on a fluid intake the 1 ml every calorie that food consumed.

For someone eat a diet the 2,000 calories every day, this adds up to 2,000 ml (roughly 64 ounces), or eight 8-ounce glasses.

However, a growing body the research argues that this wide recommendation may actually it is in too lot water for part people and also not enough for others.

While over there are certainly circumstances in i beg your pardon water needs increase, healthy world generally don’t have to be spend water in such huge quantities.

On the various other hand, not drinking enough water can reason mild dehydration, defined as the lose of 1–2% of body weight due to fluid loss. In this state, you might experience fatigue, headache, and impaired atmosphere (1).

But in bespeak to stay hydrated and also avoid mild dehydration, girlfriend don’t need to rigorously monitor the eight glasses rule — just follow your thirst.


There is no scientific evidence to support the 8×8 rule. Water requirements vary by individual, and you need to let thirst overview your intake.

the not simply plain water that gives your body v water. Various other beverages, favor milk and fruit juice, count as well.

Contrary to popular belief, caffeinated beverages and also mild alcoholic drink such as beer may additionally contribute to fluid intake, at least when they’re spend in moderation (2, 3, 4).

Many that the foods you eat also contain far-ranging amounts that water.

How lot water you acquire from food counts on the lot of water-rich foodstuffs you eat. Fruits and also vegetables are particularly rich in water, and foods choose meat, fish, and also eggs additionally have a fairly high water content.

For example, watermelon is 91% water, and eggs are 76% water (5, 6).

Lastly, tiny amounts of water are developed within her body once you metabolize nutrients. This is referred to as metabolic water (7).

People that don’t obtain much water from foodstuffs need come drink more than those that eat an ext water-rich foods.


Besides water, various other foods and also beverages friend ingest likewise contribute to your in its entirety daily input of fluids and assist keep girlfriend hydrated. Part water is likewise created within your body with metabolism.

While this may absolutely be used as a guideline, there room a variety of factors, both inside your body and also in your environment, that influence your require for water.

Body size, composition, and task level vary greatly from person to person. If you’re an athlete, live in a warm climate, or are right now breastfeeding, your water requirements boost (16).

Taking every this into account, that clear the water demands are extremely individual.

Eight glasses that water per day may be more than enough for part people, yet it might be too small for others.

If you desire to save things simple, simply listen to her body and also let thirsty be your guide. Drink water once you’re feeling thirsty. Stop once you’re not thirsty anymore. Comprise for fluid loss by drinking more during hot weather and exercise.

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However, keep in mind that this does not apply to everyone. Some older adults, because that example, might need come consciously remind themselves come drink water, since aging deserve to reduce the emotion of thirsty (17).