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Marek Struszczyk

Co-Founder ManagerUp

Last modified: June 8th, 2023

Have you tried to find an answer to “how much water should you drink a day?”

I have.

I wanted to validate the conventional wisdom that says we should drink 8 glasses of water a day.  I had a look at the recommendations of respected health institutions and medical bodies, but they are so confusing.

Just look at the list below on.

Water Intake Recommendations:

1. The National Academies of Sciences, Engineering, and Medicine

– For men: 3.7 liters or 125 ounces.  

– For women: 2.7 liters or 91 ounces.


2. World Health Organization

– For men: 2.9 liters or 98 ounces (Sedentary, Temperate Environment)

    4.5 liters or 152 ounces (Physically Active and/or Increased Temperature)

– For women: 2.2 liters or 74 ounces (Sedentary, Temperate Environment)                      

    4.5 liters or 152 ounces (Physically Active and/or Increased Temperature)


3. National Health and Nutrition Examination Survey, 2009–2012

– For men: 3.46 liters 117 ounces.

– For women: 2.75 liters or 93 ounces.


4. UK National Health Service (NHS)

– For men: 6-8 glasses.

– For women: 6-8 glasses.



– For men:  3 liters or 104 ounces

– For women: 2.1 liters or 72 ounces


6. The U.S. Dietary Guidelines 2015-2020 

These guidelines do not recommend a specific daily water or fluid intake, but they do recommend choosing plain rather than flavored water and juices with added sugar. 


As you can see, every institution gives different advice! Some do not give any specific recommendation at all…

Additionally, most of the recommendations do not say if they are for people with sedentary office jobs, like me.  Maybe they make reference to people who work physically and sweat a lot during their working day. Or maybe they are simply average numbers for general population.

Uff…It is a mess.

I thought that some articles on the internet could help solve this puzzle, but most of the posts on the Web provide us with simplistic and often contradictory recommendations.

So, I did my own research and now have a clear answer for you in this article, which will not be simplistic because body hydration is a complex topic.


Is There One Simple Recommendation on How Much Water We Should Drink a Day?


First, there is NO hard data that can support a set number of glasses per individual.  Scientists are not able to define objective, accurate measurements on how well hydrated the general US or European populations are.

Secondly, we are all varying shapes and sizes, and have unique needs dependent upon our health state.

Thirdly, our needs depend on the amount of water we lose every day, and this depends not only on our constitution, but also on where we live and what we do during the day.

But, why is it so important to supply your body with water regularly?


Why Should We Actually Drink Water Every Day?

The answer: because we lose water continually, 24 hours a day; and without water we die. Our bodies need sufficient water to function properly. Water is needed by our cardiovascular and neurological systems, by our muscles, bones, etc.

Our body water (60% of total body content) is continuously removed through:

– Breathing

– Urine and excrement

– Sweating


If you do not replenish this lost water, you get dehydrated; and this has serious consequences:

– Mild dehydration (1–2%) affects cognitive performance and memory.

– Moderate dehydration (up to 4%) makes us irritated, sleepy, increases respiratory rate, causes headaches and decreases muscle strength.

– Severe dehydration (more than 8%) may lead to death.


This means that the objective of drinking water is to compensate for the continuous loss we experience every day.

So, the answer to the question, “how much water shall I drink a day”, depends on the amount of the water you lose every day, right?

Yes, and here it gets a bit complicated…


Factors That Determine Water Loss

It is extremely difficult to determine how much water you should drink a day, because everybody loses different amounts of water.  Even the same person loses different amounts of water during two consecutive days.

Why is it, so?

Here are the most widely recognized factors that influence your water loss.

– Your job type: it is pretty obvious that a person who sits all day at a desk will lose less water (sometimes significantly less) than a person who works physically outdoor on a hot day.

– Atmosphere and temperature: If you live and work in a hot, humid environment, you will require more water. High temperature and humidity increase sweating and respiration rates. To lose less water, turn on the air-conditioning during hot summer days.


– Physical exercise: Again, a pretty obvious thing: people who exercise lose more water than couch potatoes. This water loss increases with the intensity of the exercise.

– Health Condition: Your body loses liquid when you have a fever, diarrhea or even when vomiting.


So, How to Estimate How Much Water We Lose a Day?

In the scientific literature we can find some good estimations about the water loss of average individuals.

Daily Water Balance in Your Body:


Respiratory loss                             from     – 250   to      – 350 ml/day

Urinary loss                                     from     – 500   to   – 1,000 ml/day

Fecal loss                                          from     – 100   to       – 200 ml/day

Insensible loss                                from     – 450   to    – 1,900 ml/day

TOTAL LOSS                                     from  – 1,300   to   -3,450 ml/day

Metabolic water production      from      +250   to     +350 ml/day

TOTAL NET LOSS                           from   – 1,050  to    -3,100 ml/day


Now let me explain the table:

Respiratory loss means that you lose water when you breathe. You also lose water when you visit the restroom to do your necessities.  In this case, we speak about urinary and fecal loss. Insensible loss is through the skin when you sweat.

On the positive side, our bodies also produce water during metabolism and energy production. This is what you see in the table under the “metabolic water production.”

A person at a sedentary job, with an average body size, loses each day between 1.05 and 1.5 L.

This obviously does not include any physical exercise like jogging, swimming and gym visits before or after work. This water loss (sometimes significant) is additional.

If water loss is dangerous, maybe you should drink larger amounts to make sure you are never dehydrated?


But…Does It Make Sense to Over Hydrate?

The evidence that over hydration is beneficial is not clear. Importantly, drinking too much water can be dangerous. It may even lead to death in extreme cases.

Find out Why Drinking Too Much Water Can Lead to Death


Moreover, too much water may deplete the minerals, especially potassium and magnesium, that are essential for health. It may also lead to fatigue as our kidneys must work harder. 

Slight over hydration is OK. Excess water is normally removed efficiently from the body. Of course, this does not apply to people with renal problems. They must control their water consumption with their HCP.

Over hydration may make sense If you are following a diet high in sodium; then you may need to drink more water to flush out that extra sodium that can be harmful to your body.

There are also some medical conditions like urinary tract stones and bladder infections that require more water intake. But again, always consult with your doctor.

The conclusion: it makes little sense to over hydrate unless there are specific medical indications.

It is important to remember as well that all healthy foods contain significant amounts of water. Let us have a look at the water content of different foods.


What Counts As “Water”?

You can find water in all kind of foods. So, what counts as water? Here is the answer:

1. Fruits and Vegetables

Fruits are made principally of water. A pear is 84 percent and a banana is around 74 percent, while watermelon is 92 percent water. Different organic products that are equivalent to or more than 90 percent water are fruits like grapefruit, melon, and strawberries. They also provide a wide range of minerals and vitamins.

Many vegetables have more than 90% water content. For instance, celery, lettuce, and radishes contain 95-96 percent water. Zucchini, tomato, spinach, and eggplant contain about 90%.


2. Dairy Foods

Foods such as ice-cream and yogurt are high in water content. Plain low-fat yogurt is almost 89%, while a low-fat vanilla dessert is 61% water. Indeed, even cheddar cheese has nearly 40% water content.


3. Different Sources of Water

Juices, soda, soft drinks, and smoothies can be hydrating; however, they can be high in sugar and calories. Tea, coffee and alcoholic drinks also provide water but cause you to lose more when you pee. Sports beverages have high water content. Energy drinks are not quite the same as sports drinks. They contain sugar and stimulants, similar to caffeine.

If you want to maintain a healthy diet, remember that a 30-year-old, sedentary male should aim for 2,400 calories while 30-year-old sedentary women should consume 1,800 calories per day. Be sure to avoid drinks high in calories. You may consider drinking a cup of green tea!


How Much Water Should I Drink a Day, Then?

It is clear that it does not make sense to drink too much; but not drinking enough can cause serious problems.

If you have a sedentary job, your working environment is not hot and humid, on that particular day you do not exercise, and you have a small constitution, then your daily water loss may be as low as one liter.

Assuming you have a healthy diet laden with fruits and vegetables, about 20-30% of your water requirement may be covered by the food you eat.

Therefore, a general guideline, the recommendation of 8 water glasses a day could mean over hydration. But your water loss personal. Maybe in your case 8 glasses is far too little.

Therefore, I suggest NOT to have a fixed number of glasses or bottles in mind.

Actually, assuming that you drink water regularly, it is probably more important to know WHEN to drink water than to control HOW MUCH water you drink a day.

– Follow a healthy diet loaded with lots of fruit and vegetables.

– Always drink water with meals.

– Slightly increase consumption when the environment becomes hot.

– Have a water bottle at your desk and sip slowly from time to time.

– Always replenish lost water after physical exercise (but not excessively).

– Consider increasing your current water consumption if you are obese or you have a specific medical condition. Please talk to your physician before you decide to follow this advice.  


For further advice on drinking water at workplace, please have a look at this post: “Stayed Hydrated at Work in 7 Easy Ways.”


The Bottom Line

In reality, we are losing water even through the basic act of breathing. But the exact daily water loss is very personal and depends on your body constitution and physical activity level.

Our objective should be to adjust our water consumption to our specific needs and not to adhere blindly to any specific recommendation.

Please let us know in the comments below about your personal strategy for water consumption. I am also interested to know how you have found out how much water you should drink a day.


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