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How Much Water Should I Drink? The Latest Science is Surprising

There is a lot of mystery surrounding how much water we need to drink to be healthy. Obviously, we can live without much water at all, or most of us would have keeled over by now. The real question is about optimal health. The amount of water we need for optimal health may be quite different than what we need to remain alive. There are even some research studies suggesting that drinking more water could do more than just make us head to the bathroom more often and be less thirsty. Let’s investigate.

Drink Enough Water

Yes, there are actual scientific research studies about how much water you should drink. That’s where the mystery comes in. As humans, many of us seem to lack any sort of natural instinct to determine what is the best water level intake for our optimum health. Thirst is an indicator, but then again, we have been told that by the time we are feeling thirsty we are probably already dehydrated.

They say our bodies are made up of anywhere from 55 % water, for women, 60 % for men, 75 % for babies and 80 % for potatoes. We tend to have a lower water content as we age, so babies have the most. The elderly are often down around or below 50 %.

The human body is about 60 % water. Water comes and water goes. Mostly it goes through sweat and urine. Mostly we drink it and some of it we get from our food. You’ve probably heard that we should all be drinking 8 cups of water a day. That might be true. Might not.

8 Cups a Day, Every Day – Fact or Fiction?

The 8 cups of water per day rule has been repeated so many times that it has become a mystery who even said it first. Here is a theory though about where it all started.

The Food and Nutrition Board on the National Research Council in the United States stated in 1945 that the ideal intake for adults was about 2.5 litres of water daily. That is about 8 glasses of water. So, maybe that is the origin telling us how much water to drink. That particular statement included a proviso that most of that requirement was satisifed by solid food consumption. There was no suggestion that this water intake was supposed to be in addition to normal food consumption. Nutritionists at that time also recommended that any additional requirement for fluid would be easily met by drinking other beverages, not just water.

The Mathematics of Drinking Water

There have even been complex mathematical equations designed to tell us just exactly how many glasses of water we should drink every day. Roughly, they tend to come out close to the eight glasses, but they make the appearance of using personal data to fine tune the final results to say how much water to drink. Here is an example of a complex formula. No matter your weight, or your age, be sure it is telling you that you do not drink quite enough water.

How Much Water Should I Drink?
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The Mayo Clinic tells us to drink when we are thirsty, but that some people may need those 8 glasses. There are reasons some people may need more water than others.

Harvard Medical School tells us that the 8 cups a day as a rule is essentially just nonsense. They do say, however that we need to be drinking water throughout our day in order to be sure to stay properly hydrated. We need to be staying hydrated daily, not just in special circumstances like in the blazing heat, or during high activity levels. They caution older adults to always remember to drink more water because the sense for being thirsty can slowly reduce as we get older. Many older adults are also taking medications that can cause fluid loss in addition to normal urine and sweat loss. Diuretics for blood pressure, swelling or any other reason will make an older adult more prone to needing more fluids and therefore not drinking enough water.

Water has many important functions in the human body. Some are more obvious than others. Drinking enough water will make sure your body can:

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

It is vital that we give our bodies enough water to perform all of these important tasks that require fluids. That is what staying hydrated is all about.

Water, Hydration and Health

In their abstract, Water, 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. They noted that we all need water, because without it we would die within just a few days. Since fewer people seem to be drinking water, and more are drinking beverages that are described as “caloric” they wanted to look at how much water can prevent nutrition based diseases. These “caloric” beverages are really just code for soda, but it does include sugar sweetened fruit juices as well.

We all get some water from our food. Different foods have different moisture contents so they will contribute more or less to our overall fluid intake. It is estimated that about 22% of water intake comes from food in the United States. In European and some Asian countries the estimates are higher because the typical diets there contain more fruits and vegetables. Fruits and vegetables have a higher moisture content than meats and carbs, which is a part of why they are considered to be vital for a healthy diet.

When we discuss water intake and optimal health it can be difficult since most of the information on the subject compares water intake to illness and chronic dehydration. There is lots of research that says that drinking water if you are dehydrated is a good idea. There is little research that even raises the question if we are adequately hydrated to not get sick, is there any benefit at all in drinking more water than we actually need.  There might be a level at which we are drinking enough water to not be dehydrated, but still not drinking how much water is necessary to be truly optimally hydrated. We want to know if just staying hydrated enough, is sufficient, or if there is a level that is better for optimal health.

Dehydration and the Effects on the Body

Let’s take a look first at what happens to us if we are actually dehydrated. That gives us a place to start. Once we know we are drinking enough to stave off dehydration we can decide to drink more water, daily, or at least in those situations that we are specifically likely to risk dehydration.

Physical Performance

This has actually been pretty well studied because athletes and the military are keenly interested in maximizing physical performace, and minimizing time, supplies and distractions, like drinking water would be. In high -intensity exercise you can lose up to 10% of your body weight in sweat, which is certainly dehydrating. The stats say that with as little as 2% loss your physical and cognitive performance starts to suffer. You will likely, quickly, feel more tired and percieve the activity to be more difficult than it was when you were well hydrated. Motivation reduces and you are likely to feel hot. So, when you are exercising, if the activity starts to get really hard, you feel really tired and would like to quit because you feel really hot, consider a drink of water before quitting. It may be an early sign of dehydration and you may find after a drink of water you can continue with your exercise routine.

Drink more water when exercising

Cognitive Performance

We often do not think about the fact that even mild dehydration can affect our thinking. Even being mildly dehydrated can disrupt our moods and our cognition. Since our ability to concentrate, our short term memory and alertness are all affected it makes sense that this is something to pay close attention to with school aged children. It has at least been suggested that being mildly dehydrated is a physiological stresser and that this stress could compete for our attention and our cognitive processes, while negatively impacting our mood.

Digestion and Gastrointestinal Functions

Water is exceptionally inportant to keep our digestive systems functioning well. Fluids from our foods are absorbed in our small intestines but our colons do absorb some, too.

Constipation is the most common result of not having enough water in the gastrointestinal tract. Digestion slows down making it hard to pass the small, hard stools. There are several contributiong factors, like particular illnesses, poor diet, low fiber intake and certain medications, but inadequate water can be at least a contributing factor. An increase in the amount of water you drink can be helpful to alleviate some of the symptoms, at least.

Diarrhea is a major cause of dehydration. In fact it is a leading cause of death in children. It is the resulting electrolyte imbalances that create the life threatening issues. It is best for you to keep drinking water or an electrolyte solution and not get dehydrated in the first place, but if you do, seek medical attention. It is dangerous.

Kidney Function

Our kidneys regulate the water balance in our bodies and work to maintain our blood pressure, while removing waste, too. There is a complex balance of hormones and minerals required to keep us healthy that our kidneys need water to do. They filter waste from our bloodstream using the water we drink. If we do not drink enough water we can end up with kidney stones. If you wonder if you would like kidney stones, ask anyone who has had them.

Heart Function and Blood Flow

Our blood volume is regulated as our bodies match our water intake and output. When we drink more water our heart rate is reduced and our blood pressure is increased. When we drink enough water our heart and circulatory system can remain in balance and make it possible for us to be active, without undo stress on our system. If we are dehydrated, especially when active, there is a lot of stress on our heart and circulatory system. This is why people collapse when they exercise in the heat.

Headaches and Migraines

Being dehydrated can give you a headache. It can not just trigger a regular headache but also dehydration can trigger migraines. It also can prolong a migraine that you aready have. If you have a headache that has been triggered by being dehydrated you should be able to drink a couple of glasses of water and find that the headache eases up within 3 hours, and many as quickly as within a half hour. Although that may work well, there is not much evidence that staying hydrated actually prevents the headaches, but it seems to make good sense.

Dehydration leads to headaches, studies show


An extension of the “Drink Eight Glasses a Day” myth is the myth that if you do you will have a beautiful, healthy, glowing complexion. The assumption is that by drinking more water that your skin will be less dry, more moisturized, or that acne or some other skin condition can be healed. There does not appear to be any documented evidence to support this, but there is nothing to say it does any harm to drink more water, either. There does not appear to be any evidence that being super hydrated will prevent wrinkles which come from environmental damage like sun exposure, or your genetics, either. Better to stick with a nice face lotion and sun screen, while drinking enough water.

Chronic Diseases and Not Drinking Enough Water

There is some pretty strong evidence that many chronic diseases are connected in one way or another with not drinking enough water over a long period of time. Aside from the constipation we already talked about there is quite a list of conditions that have been associated with chronic dehydration. Some are better studied than others. There need to be more studies to be sure, but check out this list.

  • Increased urinary tract infections.
  • Difficulty controlling hypertension.
  • Increased incidence in fatal coronary heart disease.
  • More severe exercise asthma.
  • Decreased control of hyper glycemia in diabetic keto acidosis.
  • Increased frequency of venous thrombo embolism – more commonly known as deep vein thrombosis, or DVT.
  • Brain damage caused by a cerebral infarct.
  • There is some evidence, although inconsistent, that keeping well hydrated may have an effect on bladder or colon cancers.

It seems safe to say that drinking enough water is a key component to good health. Exactly how much water we need, and what affect it will have on our health has yet to be determined.

Dehydration in the Short Term

Let’s look at the shorter term. Long term mild dehydration causes long term chronic diseases. We can look at a more acute case of short term dehydration to see what symptoms are similar and what are different. Because water is leaving your body constantly you have to drink enough water to make up for it. Dehydration is when more water leaves your body than you take in. It can be caused by either drinking too little, or the loss of too much fluid. Or by both.

To start, here is a checklist for deciding if the situation you are in, or are going to be in, might put you at risk for being dehydrated.

  • Heat – If you will be someplace hot, you can lose a lot of your body’s fluid through sweat. Feeling hot can be a result of being dehydrated, but being hot can be a cause. So, if it is hot outside, or you are going to hot yoga, make sure to drink extra water.
  • Intense exercising – Vigorous exercise also leads to losing fluids as you sweat. How you define vigorous may be different from someone else, but if you sweat it is vigorous enough to count as a dehydration risk.
  • Diarrhea and Vomiting – Each individually can cause significant loss of fluids that can leave you dehydrated. If you have both at the same time, this is a huge risk.
  • Nausea – Even if you don’t actually vomit, if you are nauseated you may not feel like eating or drinking. If you stop drinking, dehydration is close around the corner. Keep drinking.
  • Skin Infections and Burns – Severe burns and skin infections interfere with the natural process of sweating, and can lead to dehydration.
  • Diabetes – If you have diabetes and your blood sugars are high, your body will make more urine to help remove the sugars from your body. It seems counter intuitive to many to drink more water when you are heading to the bathroom all the time, but when it comes to diabetes it is really important. Controlling blood sugar is key though. This is why frequent urination is considered a symptom of diabetes.
  • Fever – When you have a fever you will tend to sweat. High fever or low fever it doesn’t matter. Just like exercise or being where it is hot, having a fever increases the loss of fluids through your skin, so drink up!

Dehydration is when you lose more fluid than you drink. So, when you face the situations where you lose extra fluid it is important to increase your intake of water to compensate for those losses. It is always about keeping the balance of intake and outgo. Keeping the body in balance is key.

When To Seek Medical Attention

Some mild dehydration is possible to endure and treat without medical attention. Chances are most of us do it most of the time. A few ounces of water and the short term effects are eliminated, and a daily regime will stave off the longer term effects.

At some point though, dehydration becomes dangerous. There are international protocols to deal with serious dehydration problems. People die from dehydration. It is important we can identify the signs of both mild and serious dehydration so we know when to take action.

  • Serious and extreme thirst.
  • Sleepiness outside of normal times and extreme fussiness in children and infants.
  • Irritability and / or confusion in adults. Sometimes in less extreme cases what has been called “hangry” can be staved off, at least a bit, by drinking a glass or two of water.
  • Very dry mouth. No spit. Like none. This is serious.
  • Very dry skin and mucous membranes.
  • Little or no urine produced.
  • Any urine produced will be darker in color than normal. It can get as dark as golden or even brown.
  • Sunken eyes.
  • Shrivelled and dried out skin. The skin isn’t elastic. If you pinch it into a fold it won’t bounce back to its original place.

There are other, less severe, but still important signs you may be dehydrated. These may not require medical attention, but they should still never be ignored.

  • Not sweating when you are working out. If you are doing something that should make you sweat, and you don’t, you are probably at least mildly dehydrated.
  • You have dry skin patches, especially if you normally have oily skin. It may be that you lack the appropriate oil balances in your system, but it could be water. Drink more water and look up essential fatty acids.
  • You suddenly have really bad breath. There are a lot of other causes for bad breath, but especially if your breath has suddenly gotten worse (and you don’t have a toothache), drink some more water and see if it helps.
  • You feel hungry all the time. We sometimes mix up the messages our brain sends that mean hunger and thirst.
  • You get sick a lot. If you seem to catch everything that comes around, consider a daily regime of drinking more water.
  • Even on a diet you are gaining weight. Being dehydrated slows your metabolism down so it is pretty much impossible to be losing weight when you are not drinking enough water every day.
  • Your pee is anything but clear or just a very pale yellow. If you can see your pee in the toilet, it is likely time for drinking some extra water.
  • If you are thirsty. Maybe that should have been the first thing on the list.
  • You are sleepy when you shouldn’t be for any other reason. If you are suddenly taken by the extreme need to nap, have a drink of water first.
  • You have a headache. Regular tension type headaches and even migraines often respond to some extra water. That might be why the medicines all say to take them with a big glass of water. Maybe it is the water that worked, not the pills.
  • Your handshake is cold and clammy. Yeah, yuck.
  • You have muscle cramps. There are many different reasons for muscle cramps. Often it is about the minerals that are imbalanced in your system because of the dehydration. Drink some more water in your daily regime, and have a soak in the tub.
  • Low blood pressure. Low blood volume is from not having enough blood in your body. You need fluids to increase your total blood volume. That is why the water is important for low blood pressure.

There are lots of indicators of dehydration. Some are acute and others chronic. Some are severe and life threatening and others are just annoying. All of them can be prevented by making sure you drink enough water, and drink extra in risky situations.

How Much Water You Really Need to Drink

The short answer to that question is, that depends. As long as you are drinking pure water or fresh fruit or vegetable juices then it looks like 4 glasses a day is a good minimum number. The rest of your fluid intake should be managed by a healthy diet. Now, if you know that you are not eating adequate fruits or vegetables to make up the amount you need, add some water. If you feel thirsty, have a drink of water. If you are going into a situation that is a dehydration risk, do what they call “water loading”. Drink a bunch of water before you go, and then continue to drink smaller amounts while you are in the situation.

How Much Water You Should Drink Each Day
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So, 4 glasses, plus extra for activity, hot weather, or being sick. It might end up that many people do need to drink those eight glasses that have been recommended, after all. 

How to Improve Your Water Drinking Habits

One of the best ways to improve your water drinking habits is to purchase a water filter. The psychological act of investing in a filter will subconsciously make you want to justify your purchase. Nearly all filters universally improve the taste of tap and well water, which makes it a little more pleasant for those of us with less than ideal water.

Water Filter Pitchers

Water filter pitchers are the most affordable water filters on the market and are all very effective at improving the taste of water, although they are not great at improving the safety of water and rarely remove dissolved solids. Some water pitcher filters also have alkaline water options, which may be beneficial for some people.

Countertop Water Filters

Out of sight is out of mind, so the saying goes. Buying a countertop water filter that is always full of great tasting water, in sight every time you go into your kitchen is bound to remind you to drink more water each day.

Under Sink Water Filters

Under sink water filters are the most effective way to get the purest and perfectly optimized drinking water for you home. They come in a variety of shapes, sizes and filtration effectiveness. They can ensure you not only have the best tasting water but also the safest & healthiest. The best filters in this category by a large margin are reverse osmosis systems.

Why They Keep Telling You to Drink More Water

There is a lot of cynicism surrounding this topic. If we in fact do not need to be drinking more water, or at least not the 8 glasses a day, then why do they keep telling us so? Is it just people repeating something that they heard, without fact checking? Is there some reason they want us to feel guilty or bad about ourselves and our health? Or is it the bottled water companies trying to sell more bottled water? We know there have been studies conducted by the bottled water manufacturers that found that people were not optimally hydrated. Hard to say if that counts as unbiased scientific results. Weight loss programs tell you to drink 8 or more glasses a day to help lose weight. Experts tell us that although drinking a couple of glasses of water before a meal will fill your stomach, it is likely only to make you feel uncomfortable if you still eat the larger portions. Eat smaller portions to lose weight. If drinking water helps you do that, then do that. There is still no direct evidence that excessively high water intake levels will lead to weight loss.

Margaret McCartney is examining the claims that everyone needs to drink more water. The “Hydration for Health” scientific initiative promotes drinking even more water. They are encouraging healthcare professionals to talk with their patients about what they call SSBs, or “sugar sweetened beverages”. They are looking to have medical professionals recommend drinking water as a lifestyle modification that should help people manage their weight. It sounds simple enough. Drinking water instead of sugary beverages is a good idea, and a healthy step for general health, not just better hydration. The problem here is even more simple though. Hydration for Health is sponsored by Danone. That’s the company that makes several bottled waters. So we have to ask ourselves, do we really need to drink more water, or do they just want us to drink more of THEIR water?

How Much Water Are we Actually Drinking? 

There is a joke that says if the rule for better health was to drink 8 glasses of beer a day, that would be no problem. So, why is drinking 8 glasses of water so difficult? We even resist drinking the minimum 4 glasses. The US National Library of Medicine has published a study through the National Institutes of Health that investigates just that. They have studied the “Behaviors and Attitudes Associated With Low Drinking Water Intake Among US Adults, Food Attitudes and Behaviors Survey, 2007”. What they have discovered answers a lot of questions for many of us. Their goal was to be able to specifically describe the people who do not drink much water. They also wanted to be able to figure out whatever associations there were between the attitudes and behaviors that leads to their low water intake. The hope, of course, is to be able to break the cycle of low water intake by discovering what the nature of the cycle is.

They did not do a study from scratch, but like many other studies, they analyzed data from another study that already had the information they needed. The National Cancer Institute had already completed a Food Attitudes and Behavior study earlier in the year.   Studying people’s water drinking habits does rely on what is called “self- reporting”, which just means that they ask people how much water they drink and accept their answers as true. They were focusing on the people who said that they drank less than 4 cups of water a day. Here’s the statistics they found.

  • 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.

So, less than half of us say we drink less than 4 cups a day. The study was about making the connection between who drinks very little water and why they drink so little. By describing the people who drink the least and the most perhaps we can get some insight.

  • People over 55 years old are most likely to drink less than 4 cups of water a day.
  • Adults who are 18 to 34 years old are the most likely to drink more than 4 cups of water a day.
  • People who live in the northeastern part of the United States are least likely to drink enough water.
  • Residents of the southern United States are the most likely to drink enough water. Perhaps this one is as simple as the fact it is hot outside more often in the south than in the northeast.
  • Individuals whose diet included one cup, or even less, of fruits and vegetables on average per day are also least likely to drink enough water.
  • Individuals whose diets included more than four and a half cups or more of fruits and vegetables a day were most likely to be drinking enough water.
  • If the person reported that they did absolutely no exercise at all, they were most likely to also report that they did not drink enough, or any water.
  • When a person reported that they had a regular exercise program of more than 150 minutes weekly, they also reported that they were most likely drinking more than 4 cups and often more than 8 cups of water, a day. In fact, 7 X more likely than someone who was not exercising at all.
  • Participants who were not on a diet to lose or gain weight were less likely to report that they drank enough water.
  • Those participants who were on a diet to lose weight were also far more likely to be drinking more water.
  • The overall statistics say that the mean amount of plain water that US adults over 20 years old drink is 4.3 cups or 34.4 ounces for the women 4.4 cups or 35.2 ounces for the men.

The general conclusion then is that not drinking enough water seems to be associated with other unhealthy attitudes, getting older and living in the northeast. Chances are moving out of the northeast is not on the table for a change, and getting older doesn’t seem to be much of a choice. As such, choosing a healthy lifestyle in a general sense, and therefore drinking enough water, too, seems to be the most desirable result. Overall, though, most people seem to actually be getting their 4 cups a day, plus whatever they get from their food.

Plain water has no calories in it so it is an excellent choice to replace beverages that are high in calories and sugar. It makes it easier to maintain a healthy body weight and reduces the chances of cavities in the teeth, or other chronic diseases that are associated with excessive sugar intakes, especially when accompanied by low water intake. Dehydration is connected with several acute symptoms and chronic diseases, none of which are desirable. From depression and constipation to kidney stones and cavities, drinking water is just a good idea for our healthy lifestyles.

If you are concerned that you may not be drinking enough water, here are some ideas to make it easier to drink more.

  • Keep your water bottle with you. Make sure you can access it easily, and keep it full. Keep it on your desk, in the car, or nearby where you sit to watch TV. Keep it in arm’s reach. Have more than one.
  • If you like your water really cold, freeze some freezer safe water bottles. Be sure to keep the cap off until they are frozen. Take one along for cold water all day.
  • Any time you would reach for another beverage, at least drink some water first. Drink a glass of water before having your coffee, tea or soda, if you are unable to completely replace it. Missing one 20 ounce sweetened soft drink will save you 240 calories. That’s a one hour walk for exercise to burn that 240 calories off. Try the water instead. Go for the walk anyway. Then have more water.
  • Have water when you eat out. It reduces calories and usually saves you some money.
  • Add some fruit or vegetables to your water bottle, or to a jug in the fridge. Lemon or lime or orange are really good. Some people like cucumber or mint as well. Mix and match. Check out some recipes online. You can make water taste even more delicious when you add some fresh fruits, vegetables and herbs.

In case it hasn’t been made clear quite yet, drink water. Drink at least 4 glasses every day. Make it part of your routine so there is no forgetting. Drink extra water, “water loading”, before you are going into a risky situation like high activity, high heat or you are sick, chronically or acutely and continue to drink smaller amounts throughout your day. Think about how much water you drink every day.

It may be that there is not quite enough evidence that drinking enough water really does cure or prevent every possible medical condition, but there is no evidence that it ever does any harm. So, stay hydrated, and be well.



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