The Amount of Water You Should Drink According to Science

The question ‘how much water should you drink daily in order to be healthy?’ has never had any concise answer. The fact of the matter is, we can live without drinking a lot of water at all, so the real question is about optimal health. To be at optimum health, the amount of water we need daily may be quite different from what we need to stay alive(remember that these two are very different). Quite a few researches suggest that if you drink more water, there are other effects than heading to the bathroom more often and be less thirsty. Let’s find out.

There are scientific research studies about how much water you should drink daily that have been done. As humans, a lot of us seem to lack any sort of natural instinct to determine what is the best water level intake for our optimum health. We usually rely on thirst is an indicator. The problem is, we have been told that by the time we are feeling thirsty, we are probably already dehydrated. So, naturally, that instinct isn’t very reliable. The fact is, our body is made up of anywhere from 55 % water, for women, 60 % for men and 75 % for babies. The tendency is that we the water content will become lower as we age. So naturally, babies will have the most water in their body. When we are around 60 years old, it often goes down around or below 50 %. The human body is made of about 60 % water. Take note that water comes and goes every day. It mostly goes through sweat and urine and the more we drink, the more comes out. Our main source of water is from what we drink and from what we eat(albeit this is a very small percentage). By now, you should have already heard that we should be drinking 8 cups of water a day. This might or might not be true.

Is 8 Cups a Day True or False?

You’ve probably heard of the rule 8 cups of water per day because it has been repeated so many times. The theory about where it all started comes from The Food and Nutrition Board on the National Research Council in the United States. They said in 1945 that for adults, the ideal intake for was about 2.5 litres of water daily. That roughly translates to 8 glasses of water(depending on the size of the glass). This is probably the origin of where that rule came from. That statement included a condition that most of that requirement was satisfied by solid food consumption. But in fact, there was no suggestion that this amount of water intake was supposed to be in addition to normal food intake. At that time, nutritionists also recommended that any additional requirement for water would be easily met by drinking other beverages, not just regular water.

Mathematics of Drinking Water Daily

Mathematics has also been used to calculate the daily recommended water intake. There are complex mathematical equations designed to tell us just exactly how many glasses of water we should drink every day. Although it results into roughly around eight glasses too, it does make it  appear that the use of personal data to fine tune the final results will say how much water to drink daily. Let’s take a look at the complex formula. (*infographics)

Although the Mayo Clinic tells us to drink when we are thirsty, there are reasons that some people may need more water than others. The Harvard Medical School says that the 8 cups a day rule is just really nonsense. But, they did say that we need to drink water throughout our day in order to stay properly hydrated. Proper hydration is important not just in special circumstances like in the blazing heat or during high activity levels. They also warn older adults to always remember to drink more water because as we get old, the sense of being thirsty can slowly reduce. A lot of older adults are also taking medications that can cause fluid loss in addition to normal urine and sweat loss. Medication for blood pressure, swelling or other reasons will also make an older adult more prone to needing more fluids.

Water is very important for our body. By drinking enough water, you will make sure your body can:

  • Maintain the electrolyte and sodium balance
  • Regulate body temperature
  • Protect tissues and organs
  • Cushion joints
  • Protect spinal cord and nervous system
  • Stabilize heartbeats
  • Normalize blood pressure
  • Prevent constipation
  • Aid in general digestion
  • Flush harmful bacteria from the bladder
  • Carry oxygen and nutrients to your cells to your whole body

These are reasons why it is vital that we give our body enough water to make sure it performs all of these important tasks that require fluids. This is the importance of proper hydration.

Hydration and Health

Irwin H Rosenberg, Kirsten E. D’Anci and Barry M. Popkin examined the physiological effects of water on the different body systems. In their abstract, Water, Hydration and Health, they found that we all need water, because without it we would die within just a few days. The tendency today is that fewer people are drinking water and more are drinking beverages that are described as “caloric”. That is why they wanted to look at how much water can prevent nutrition based diseases. In their study, these “caloric” beverages are just code for soda and other sugar sweetened fruit.

We all get a little bit of water from our food. Remember that different types of foods have different moisture contents, so they will contribute more or less to our overall fluid intake. In the United States, it is estimated that about 22% of water intake comes from food. In Europe and some parts of Asia, the estimates are higher because their typical diets include more fruits and vegetables. The reason why fruits and vegetables are considered healthy is because they have a higher moisture content than meats and carbs(aside from the various nutrients you get of course).

So when we talk about water intake and optimal health, it is really hard to get most of the information on the water intake to illness and chronic dehydration. There are plenty of research that find that drinking water if you are dehydrated is a good idea. There are fewer research that even raise the question that if we are adequately hydrated, the lesser chances of getting sick and if there is really any benefit at all in drinking more water than we actually need. So, to think that there is a level at which we are drinking enough water to not be dehydrated is really not wrong. But it still doesn’t answer the question of how much water is necessary to be truly optimally hydrated. Knowing if just staying hydrated enough, is sufficient, or if there is a level that is better for optimal health can make a difference.

What are the effects of dehydration on your body?

What happens to your body when you become dehydrated? Before you can really appreciate the benefits of drinking enough water every day, you have to learn what happens when you are not hydrated properly. So here are the effects of becoming dehyrdated.

Physical Performance

Athletes and the military are very interested in maximizing their physical performance, that’s why this has actually been pretty well studied. During exercise, especially high-intensity ones, you can lose up to 10% of your body weight in sweat. This can cause dehydration. According to the numbers, with as little as 2% loss, your physical and cognitive performance will begin to suffer. You will most likely feel more tired and feel the activity to be harder than it was when you were well hydrated. If you are exercising and you feel that the routine is starting to get really hard, you feel really tired and you feel really hot, stop and take a break. Drink water and wait a few minutes before quitting. It might just be dehydration taking its toll. You may find that after drinking water, you can go back to your routine and finish it.

Cognitive Performance

As mentioned above, when we become dehydrated, our cognitive performance also suffers. The truth is, even mild dehydration can affect our thinking. It can disrupt our moods and our cognition. Our ability to concentrate, our short term memory and alertness are all affected when we are not drinking enough water. There are suggestions that being mildly dehydrated is a physiological stresser and will cause us to divert our attention and our cognitive processes, while also negatively affecting our mood.

Gastrointestinal and Digestion Functions

Water is very important to help keep our digestive systems functioning properly. Fluids from the food we eat are absorbed by our small intestines and our colons.

The most common effect of not having enough water is constipation. This is because digestion will slow down, making it hard to pass the small, hard stools. There are also other contributing factors, like illnesses, poor diet, low fiber intake and certain medications. Increase your water intake can helpful alleviate some of the symptoms, at the very least.

One main cause of dehydration is diarrhea. It is even the leading cause of death in children. It will result in electrolyte imbalances that will lead to life threatening issues. That is why if you need to keep drinking water or an electrolyte solution when having diarrhea.

Kidney Function

The main function of our kidneys is to regulate the water balance in our body, work to maintain our blood pressure and remove waste. Since kidneys filter waste from our bloodstream using the water we drink, if we do not drink enough water, we might end up with kidney stones. If you are wondering what kidney stones feels like, just ask anyone who has had them. Spoiler alert: you won’t like the answer.

Blood Flow and Heart Function

The volume of our blood is regulated as our bodies match our water intake and output. If we drink more water, our heart rate will be reduced and our blood pressure is increased. When our water intake is enough, our heart and circulatory system can stay balanced and allows us to be active, without causing too much strain on our system. If we become dehydrated, especially when being active, our heart and circulatory system is put under a lot of stress. This is the reason why people collapse when they exercise in the heat.

Migraines and Headaches

If you are dehydrated, you will most likely have a headache. Dehydration can also trigger migraines and prolong them(if you already have one). If you are experiencing a headache that has been triggered by dehydration, the headache eases up within 3 hours after you drink a couple of glasses of water. It is important to note though that there is not much evidence that staying hydrated will actually prevent the headaches.


The assumption that by drinking more water, your skin will be less dry, more moisturized, or that acne or some other skin condition can be healed doesn’t have any documented evidence to support it. Although there doesn’t seem to be any evidence that being hydrated properly will prevent wrinkles which come from environmental damage like sun exposure, or your genetics, it is till a good practice to stay hydrated. If you want to avoid wrinkles, better to stick with a face lotion and sun screen.

Relation Between Not Drinking Enough Water and Chronic Diseases

There is strong evidence showing that in one way or another, a lot of chronic diseases are connected with not drinking enough water over an extended amount of time. Aside from constipation which was mentioned above, there are several conditions that have been linked with chronic dehydration. Here’s the list:

  • Urinary tract infections
  • Difficulty controlling hypertension.
  • Increased chance of fatal coronary heart disease
  • Severe exercise asthma
  • Failure to manage hyperglycemia in diabetic ketoacidosis
  • Increased frequency of deep vein thrombosis
  • Brain damage due to cerebral infarct
  • May have an effect on bladder or colon cancers(evidence is inconsistent).

This is why it is safe to say that drinking enough water is a vital factor to maintaining a good health. The exact amount of water we need and what effects it will have on our health doesn’t have any concrete answer just yet.

Short Term Dehydration Effects

Long term mild dehydration can cause long term chronic diseases. Since water is leaving your body constantly, you have to make up for it by drinking enough water. Dehydration happens when there is more water leaving your body than you are taking in. There are two main causes, either by drinking too little or the loss of too much fluid(or possibly both). Let us look at a more acute case of short term dehydration so we can see what symptoms are similar and what are different.

Here’s a checklist for deciding if the situation might put you at risk for being dehydrated:

Heat – Heat can cause to you to lose a lot of your body’s fluid through sweating. If you feel hot, it can be a result of being dehydrated, but being hot can also be a cause. That is why if it is hot outside, or if you are going to do hot yoga, make sure to drink extra water.

Intense exercise – High intensity exercises can also lead to loss of fluids by sweating. The definition of high-intensity may be different from someone else, but the main thing to consider is if you sweat vigorously, that is enough to count as a dehydration risk.

Diarrhea and/or Vomiting – Each condition can cause significant loss of fluids that can leave you dehydrated. If you are experiencing both at the same time, it can be a huge risk and more serious measures need to be taken.

Nausea – If you are nauseated, you may not feel like eating or drinking. When you stop drinking water, you might get dehyrdated. So make sure to keep drinking water.

Skin Infections and Burns – Skin infections and severe burns will interfere with the natural process of sweating which can lead to dehydration.

Diabetes – When you have diabetes, your blood sugar is high. It will cause your body to make more urine to help remove the sugar from your body. Although it might seem counter intuitive to drink more water(since you will be urinating most of the time), when it comes to diabetes, it is really crucial. This is because you need to control your blood sugar.

Fever – When you are having a fever, the tendency is, you will sweat more. It doesn’t matter if you are having high or low fever, having a fever will increase the loss of fluids through sweating.

When you experience these situations, it is important to increase your water intake to make up for the loss. Remember that staying hydrated is always about keeping the balance of water intake and water loss.

When Do You Need Medical Attention?

Mild dehydration can be endured and treat without any medical attention. All you need is a few ounces of water and the short term effects will be gone. A daily routine will also hold off the long term effects. There comes a point though that dehydration will become dangerous. People can die from it if left untreated. That is why there are international protocols to deal with serious dehydration problems. To be aware that it is happening, we need to be able to identify the signs of both mild and serious dehydration so we know when to take action. Here’s the list:

  • Severe thirst
  • Getting sleepy out of normal times
  • Extreme fussiness in children and infants
  • Becoming irritable and/or confused(adults)
  • Very dry mouth that will cause absence of saliva
  • Very dry skin and mucous membranes
  • Little or no urine produced
  • Urine produced will be darker in color than normal
  • Sunken eyes.
  • Shrivelled and dried out skin

There are also less severe(but just as important) signs that you are dehydrated. Although these signs may not require medical attention, they should never be ignored.

Not sweating when you are exercising

Having dry skin patches, especially if you have oily skin normally. This can be because you lack the appropriate oil balances in your system, or it could be water.

Sudden really bad breath

Feeling hungry all the time

Getting sick a lot

Gaining weight even on a diet. Dehydration slows your metabolism down.

Your urine is not clear or just a very pale yellow. If you can distinguish your urine in the toilet, then it’s time to drink more water.

Feeling thirsty

Feeling sleepy when you shouldn’t be

You have a headache(not every time though. try drinking water if you have a headache. If it goes away after a couple of hours, then you are mildly dehydrated)

Hand is cold and clammy

Muscle cramps

Low blood pressure

There are many signs of dehydration, some are severe and others chronic. These signs can be life threatening or just annoying. But regardless, these signs should not be ignored. That is why you need to drink enough water to prevent being dehydrated and developing any more risky conditions.

Amount of Water You Really Need to Drink

So how much water do you really need to drink? This question has been asked in this article several times now. The simple answer is, that depends. If you are drinking pure water and/or fresh fruit or vegetable juice, then 4 glasses a day is a good minimum number to start with. You can then manage the rest of your fluid intake through a healthy diet. If you are not eating enough fruits or vegetables, then compensate by adding more water. The basic rule is, if you feel thirsty, then drink water. If you anticipate that you will be in a situation that is a dehydration risk, then drink a lot of water before you go. This is called “water loading”. But make sure you don’t stop there. Continue to drink smaller amounts while you are in that situation. So, to sum it up, that is 4 glasses of water, plus another extra for activity, hot weather or if you are sick. You might wind up needing to drink eight glasses that have been recommended, after all.

Improving Your Water Drinking Habits

If you really don’t drink a lot of water every day, it’s time to change that. It is best to develop a water drinking habit to make sure you stay well hydrated every day. One good way to start that habit is to invest in a filter. This act will subconsciously make you want to justify your purchase and will cause you to drink more water. Best of all, most filters will universally improve the taste of tap and well water, which is more incentive to drink more water.

Water Filter Pitchers – If you do not have the budget, you can instead go for water filter pitchers since they are the most affordable water filters on the market today. They are all very effective at improving the taste of water but not as much at improving the safety of water because they rarely remove dissolved solids. There are high-end water pitcher filters that have alkaline water options, which can be good for some people.

Countertop Water Filters – Having a countertop water filter will become a great reminder for you to drink water because it is always in sight every time you are in the kitchen. Plus, countertop water filters provide great tasting water.

Under Sink Water Filters – If you are looking for the most effective way to get the purest and perfectly optimized drinking water for your household, then an under sink water filter is the only option. It comes in a variety of shapes, sizes and filtration effectiveness, but all will provide the same thing, pure and clean drinking water. Best of all, every drop of water coming out of this filter will taste great. If you have the budget, go for reverse osmosis filters as they are considered to be the best filters in this category by a large margin.

Why Do They Keep Telling You to Drink More Water?

We already know that there have been several studies conducted by bottled water manufacturers and all of them  found out that people were not optimally hydrated. Although it might not sound like an unbiased scientific, it does tell the truth. If you’ve ever had any weight loss program, it always tells you that you need to drink 8 or more glasses a day to help lose weight. This is mainly because drinking a couple of glasses of water before a meal will fill your stomach, which will then result in you eating less. The simple truth is, eating smaller portions will help you lose weight and if drinking water will help you do that, then by all means, do that. But for your information, there is still no direct proof that drinking a lot of water will lead to weight loss.

There are a lot of medical professionals and organizations, as well as bottled water manufacturers, who keep recommending that drinking water as a lifestyle change that should help people manage their weight. The logic is simple. Drinking water instead of sugary beverages is really a good and healthy idea. Doing so will help prevent serious medical conditions and will promote a better overall health. But sometimes, we have to ask ourselves, do we really need to drink more water? Or do these people just want us to drink more of their water? It’s a business after all.

What is the actual amount of water that we really drink?

Why is drinking 8 glasses of water a day so difficult? This is a question that really needs an answer. Fortunately, the US National Library of Medicine published a study through the National Institutes of Health that answers that question. Aside from that National Cancer Institute also completed a Food Attitudes and Behavior study. These studies focused on people’s water drinking habits and relied on what is called “self- reporting”. This means that whatever data they got came from what people answered and they accepted as the truth, regardless if it is or isn’t. The focus was on the category of people who said that they drank less than 4 cups of water a day. Here are the numbers:

  • Zero cups of water a day – 7 % of adults
  • 1 to 3 cups of water a day – 36 % of adults
  • 4 to 7 cups of water a day – 35 % of adults
  • 8 cups of water a day or more – 22 % of adults

The numbers show that less than half of the people drink less than 4 cups a day. Since the study was about finding the connection between who drinks very little water and why they drink so little, the best way to get some insight is by describing the people who drink the least and the most.

  • Adults 55 years old and above are most likely to drink less than 4 cups of water a day.
  • Adults who are 18-34 years old are the most likely to drink more than 4 cups of water a day.
  • Geographically speaking, people who live in the north-eastern part of the United States are least likely to drink enough water.
  • Southerners were the most likely to drink enough water. This is mainly because the temperature in the south is higher than the northeast.
  • People with a diet that included one cup or less of fruits and vegetables on average per day are also least likely to drink enough water.
  • People with a diet that included more than four and a half cups or more of fruits and vegetables a day, were most likely to be drinking enough water.
  • People who did not exercise at all were most likely to report that they did not drink enough, or any water.
  • People who had a regular exercise program of more than 150 minutes weekly, reported that they were most likely drinking more than 4 cups and often more than 8 cups of water, a day. The number was actually 7 times more likely than someone who was not exercising at all.
  • People who were not on a diet to lose or gain weight were also less likely to report that they drank enough water.
  • People who were on a diet to lose weight were also less likely to be drinking more water.
  • In summary, the average amount of plain water that US adults over 20 years old drink is 4.3 cups or 34.4 ounces for the women and 4.4 cups or 35.2 ounces for the men.

So based on the numbers and the behavior presented, the general conclusion is that not drinking enough water can be associated with other unhealthy habits, getting older and living in the northeast. Since moving out of the northeast is not really a practical option and getting older isn’t really a choice, that leaves us with developing healthy habits. By doing so, you will also be driven to drink enough water. So, to answer the question how much water we drink, most people seem to drink 4 cups a day, plus what they get from their food.

Since plain water doesn’t contain any calories, it is an excellent choice to replace beverages that are high in calories and sugar. This will make it easier for you to maintain a healthy body weight and reduces the chances of teeth deteriorating, or other chronic diseases that are caused by excessive sugar intake. Dehydration is related to several acute symptoms and chronic diseases which are not good. The bottom line is, drinking water is good for your health.

Now if you are worried that you may not be drinking enough water, here are some things you can try to help you develop the habit of drinking more water.

  1. Always carry a water bottle with you no matter where you go. Make sure you can easily access it and is always full. An empty water bottle doesn’t make sense does it?
  2. If you like cold water, make sure to get a freezer-safe water bottle so you can freeze it. Make sure to keep the cap off until the water is frozen. You can always carry it along all day and have access to cold water.
  3. Drink water first before you drink any other beverage. Make it a habit to drink a glass of water before drinking a cup of coffee, tea or soda. Remember that not drinking a 20-ounce soft drink will save you 240 calories. If you equate that to the time you need to burn it, it roughly takes one hour of walking to burn 240 calories. A better option is to drink water and go for the walk anyway.
  4. When you eat out, replace your beverage with a glass of water. Not only will you be saving calories, you will also save some money.
  5. Adding fruits or vegetables to your water bottle or jug in the fridge can make your water taste more delicious. Lemon, lime or oranges are really good options. Others also prefer cucumber or mint. Try experimenting with them and see which one you prefer.

If it is not clear to you yet at this point in the article, drinking water is good for you. Make it a point to drink at least 4 glasses every day. Make it a habit so that it will become effortless. Start and end your day by drinking water. And remember, drinking extra water or “water loading” as it is otherwise called, before you go into a dehydration-risk situation like high activity or high heat is recommended. If you are sick, chronically or acutely, make it a point to drink smaller amounts of water throughout your day. There might not be clear-cut proof that drinking enough water can cure or prevent every possible medical condition, but there is also no evidence that it doing so will cause any harm. So, if I were you, stay hydrated if you want to stay healthy.