Do You Really Need to Drink 8 Glasses of Water Daily?

Do You Really Need to Drink 8 Glasses of Water Daily?


You’ve probably heard, at some point, that you need to drink eight or more glasses of water daily. However, you still might have problems drinking this amount of water daily. You might also wonder whether this recommendation holds up under scrutiny. How did the idea of 8 glasses of water daily get started and is the recommendation to drink this much water really backed by science?

No doubt, water is essential for health and to sustain life. After all, your body is 70% water. You can live for weeks without food but only a few days without water That’s how important water really is! Yet, we often get busy and forget to hydrate. Are you really hurting your body when you don’t drink water throughout the day?

Do You Really Need 8 Glasses Of Water Daily?

The truth is the recommendation to drink 8 glasses per day isn’t supported by scientific evidence and is a bit over-simplistic. The quantity of water you need daily depends on a number of factors, including your activity level, the temperature of your environment, how active you are, and even what medications you’re taking. Some meds are diuretics and increase your fluid requirements. If you work out intensely or live in a hot environment, you may need more than 8 glasses of water daily, whereas if you’re sedentary and eat a lot of foods with high water content, you need less. If you eat lots of fruits and vegetables, especially raw ones, the food you eat can be a substantial source of water.

Still, don’t underestimate the importance of staying hydrated. You’re constantly losing fluid through sweat, urination, bowel movements, and through breathing. Yes, the fluid you lose needs to be replaced but there’s really nothing magical about drinking 8 glasses daily. For some highly active people, this may not be enough and for others, it might be overkill.

How did the whole idea of drinking 8 glasses of water a day get started? This recommendation dates back to 1945 when the United States Food and Nutrition board issued it. However, it wasn’t based on specific scientific research and it also failed to account for the water we naturally get from the foods we eat, especially plant-based foods as well as individual variations in fluid requirements based on health and environmental factors.

You may have also seen sources stating that drinking more water helps your body detoxify and has other health benefits. Some sources state that consuming more water speeds up your metabolism or helps with weight loss. While drinking more water helps your body eliminate water-soluble toxins, most of the toxins that pose a threat are fat-soluble and drinking more water won’t help you flush these. These toxins are handled mainly by your liver. How about the impact of drinking water on weight loss? Research is mixed. Some studies show that drinking water before a meal reduces calorie consumption at that meal, while other studies show no benefit. One study showed drinking water before a meal reduces calorie consumption in older people but not those under the age of 35.

Despite the lack of scientific evidence to support drinking a specific quantity of water daily, taking steps to stay well hydrated has certain benefits that ARE backed by science including:

·       Drinking more water may ward off fatigue. Even mild dehydration can cause you to feel tired, based on research.

·       Staying hydrated may help control certain types of headaches if you’re prone to them, especially tension headaches. Mild dehydration can sometimes bring on a mild headache.

·       Drinking water throughout the day helps prevent constipation, based on a number of studies.

·       Drinking more water is linked with a lower risk of kidney stones. Squeezing lemon in water adds citric acid, which also helps prevent the formation of kidney stones.

·       Staying hydrated can help exercise performance. Studies show that exercising in a mildly dehydrated state leads to early fatigue and reduced performance, especially for endurance exercise.


Staying Hydrated During Exercise

Even if you don’t subscribe to the 8 glasses of water daily theory, exercise hydration is vital for performance and for safety reasons. During exercise, your core body temperature rises and blood flow to the surface of your skin increases as your body tries to release extra heat. One way it releases heat is through sweating. You can lose a substantial amount of water and electrolytes during a long or intense exercise session, especially if you’re working out in a hot environment. During exercise, you shouldn’t depend on your thirst mechanism to tell you when to drink. For safety reasons, it’s best to monitor your fluid status closely and take steps to ensure you stay hydrated.

Here are some guidelines:

·       Hydrate prior to a workout by drinking 18-20 ounces of water two hours beforehand.

·       Drink an additional 8-ounce glass of fluid 30 to 45 minutes beforehand.

·       During your sweat session, sip another 8 ounces every 15 minutes during your workout.

·       After your workout, drink another 8 ounces within 30 minutes.

You can check your urine color to determine if you’re adequately hydrated. If you’re well hydrated, it should be pale yellow or clear in color. Another approach is to weigh yourself before a workout and immediately after. For every pound you’re down, drink 20 ounces of fluid.

During long periods of exercise, 90 minutes or longer, hydrate with an electrolyte-rich beverage rather than water. You lose fluid and electrolytes, like sodium chloride, and potassium, when you exercise. If you just replace the fluid you lost with water, your sodium level can drop too low due to the dilutional effect of the electrolyte-free fluid. This can lead to a life-threatening drop in sodium concentration. In fact, marathon runners have died from this condition, which is called dilutional hyponatremia.

The Bottom Line

There’s nothing magical about drinking eight glasses of water daily. Your fluid requirements may be higher or lower based on the factors just discussed. However, it is important to monitor your fluid status, especially if you exercise. One way to do that is to note the color of your urine throughout the day. Also, if you’re feeling tired or have a headache, try drinking a few glasses of water.



Eur J Neurol. 2005 Sep;12(9):715-8.
Cochrane Library. “Water for preventing urinary stones”
ACE Fitness. “How Hydration Affects Performance”
MedLine Plus, “Low Sodium Level”
New York Times. “The Claim: Drinking Water Before Meals Aids Weight Loss”


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