How Much Water Should I Drink a Day? The Truth Behind Water Consumption

hydration testHere’s a common question: How much water should I drink a day?

Hmmm. Well, we’ve all heard the same cookie-cutter advice…

You need to drink 8 glasses of water per day.


I mean, sure, water is important. But is it that important? Do you really need that much of it?

Well, since I’m naturally curious and I have some not-so-serious trust issues, I figured I would do some digging around and test things out for myself to finally uncover the truth behind water consumption.

Let’s just say the findings were beyond intriguing…

Before I get into the details, let me give you a little background about how all this got started.

As often is the case, the spark came from a book (I love books) and this time it’s one of my favorites – the Primal Blueprint by Mark Scisson. In the book, Mark spends some time talking about hydration and the excessive attention it’s gotten over the years.

But perhaps it’s attention well deserved.

At the same time, I was laser focused on consuming more water than most could carry. After all, I’ve always been told (as an athlete and health nut) that more water means better health. So when I happened to read that this may not necessarily be true (according to Scisson), it sparked something inside of me to dig a little deeper and get to the truth.

So I did some a lot of research and came up with some interesting facts.

Water is everywhere. I mean think about it. Everything is composed of water. Our planet is 70% water. Our bodies are roughly 60% water. Many of the things that we consider to be solid are actually mostly composed of water.

Plus the list of benefits of consuming water are through the roof.

Healthier skin. Better lubrication of joints and muscles. Better regulation of body temperature. Detoxification. More energy and alertness. Better transportation of nutrients and oxygen to cells (plus better absorption of these nutrients). Improved metabolism.

I could go on forever.

But the question isn’t whether drinking water is beneficial. You’d be a fool to think it’s not. The real question is how much water is necessary. How much water should I drink a day? Where does the diminishing effect come into play?

The 8 by 8 Guidelines

The 8 by 8 rule simply states: drink eight 8-ounce glasses of water per day (64 ounces of water total). For proponents of the metric system, this is roughly 1.9L of water per day.

But where exactly did the 8 by 8 rule come from? That’s actually a very good question and one very few people will be able to answer. Nobody really knows much about the origins of this ideology. Even many of the top nutritionists in the world can’t tell you where it comes from and they’ve written books on the topic of water!

Perhaps it’s just a convenient reference point. Professor Heinz Valtin from Dartmouth Medical School who specialized in kidney research spent over 40 years studying the systems that keep water in our bodies balanced says that the 8 by 8 rule actually originated from a misunderstanding. Back in 1945, the Food and Nutrition Board (now part of the National Academy of Science’s Institute of Medicine) suggested that a person consume one millimeter of water for each calorie of food. So, for a typical 1900 calorie per day diet, this comes out to 1900 milliliters of water per day, or roughly 64 ounces.

Dr. Margaret McCartney speculates that this ‘guideline’ is a complete myth that is being propagated by bottled water companies who are in the interest of sucking in profits.

“There are many organizations with vested interests who would like to tell doctors and patients what to do. We should just say no.” – Dr. Margaret McCartney [ref]

She gives an interesting example. There is a new international health initiative called “Hydration for Health,” which promotes drinking more water for a healthier lifestyle. Guess who it’s sponsored by? You guessed it, Danone – a company that markets the Evian and Volvic bottled water brands.

Next up, we have the Institute of Medicine which has basically decided to put the 8 by 8 rule on steroids. They have determined that an adequate intake for men is roughly around 3.7L and for women around 2.7L (even more if you’re pregnant). That’s a lot of water my friends.

But drinking more water is good, right?

Well, according to a study published in the British Medical Journal, drinking eight glasses (or more) of water does not deliver on the promised health benefits. In fact, drinking too much water can have detrimental effects on your health, including a condition known as hyponatremia (a low-blood-sodium condition). This is a serious (and occasionally fatal) condition that results when excessive water consumption per day causes sodium levels in the bloodstream to become too diluted.

“If you’re drinking excessively, if you’re drinking beyond thirst, if you’re drinking beyond comfort, your kidneys are actually having to work very, very hard.” – Dr. Margaret McCartney [ref]

So how much water should you drink a day, you ask?

Well, it depends on a few factors.

“Water requirements depend so much on outside temperature, activity levels and other factors that there isn’t one rule that fits everybody,” says Barbara Rolls, a professor of nutrition sciences at Pennsylvania State University.

Indeed this is true. If you exercise or engage in sweat-inducing activities, you need more water. If you live in areas that are more hot or humid throughout the year, you need more water. If you’re sick (fever, vomiting, diarrhea), you need more water. If you’re pregnant, you need more water.

But even with all these factors and our wide variation in water intake, the human body is very capable of maintaining normal blood concentration. Your kidneys and endocrine system work very efficiently to promote optimum fluid levels in your bloodstream.

Dr. Valtin and other experts have found that if your blood becomes concentrated by about two percent, your thirst mechanism becomes activated and you’ll feel thirsty. Once your blood becomes concentrated by five percent, the symptoms of dehydration become present.

What about food and other drinks?

Most people don’t realize how much fluid they obtain from the food that they eat. On average, food provides about 20 percent of our total water intake [ref]. Chicken is over 50 percent water. Pizza is 50 percent water. Raw milk is 90 percent water.

According to this article, there are no restrictions on the maximum amount of water a food can contain (although it must be on the label).

Remember the whole profit ordeal? It plays a factor here too.

Apart from the natural water in foods, manufacturers tend to add water to (cheap) foods to increase their weight so they can be sold for more profit.

“Consumers are being duped by manufacturers who are adding water to bulk up the size and weight of produce, and what’s worse, it isn’t possible to work out from the label how much water has been added.” – Ian Tokelove of the Food Commission.

What about checking out your urine?

We’ve all been told to take a look at the stream of urine that comes from our you-know-what. If it’s dark, you need to drink more water. If it’s clear, you’re good. Right?

Well, according to Dr. Valtin, there is no validity ot the idea that your urine needs to be clear to indicate adequate hydration.

So what do we do?

Some say that the best advice is to let your thirst be your guide.

Mark Scisson, author of Primal Blueprint, says:

“I recommend consuming a sensible amount of fluid each day, using your thirst as a guide to maintain optimum hydration. Sometimes this might be eight glasses of water, sometimes much less than half that.” – Mark Scisson

Some studies don’t agree.

Some say this isn’t effective because apparently so many people are chronically dehydrated that they no longer recognize their body’s signal for water.

But, of course, there are other studies (some done by Dr. Barbara Rolls) that show no evidence of people being chronically dehydrated.

I hope you’re confused as I am.

In an effort to set things right (at least for myself) and determine how much water I need to drink per day, I figured it was time to do a little test…

The 30 Day Hydration Test

With all this confusion, I thought it would be best to do a little of my own testing. I put together a simple little test which I like to call the 30 day hydration test. It didn’t require any crazy laboratory equipment, test specimens, or expensive tools. Actually, it barely required anything at all.

All I wanted to do was see if my body reacted differently to when I drank a lot of water compared to when I drank very little water over a (somewhat longer) period of time.

Here’s how it worked.

For the first 15 days of the test, I drank the Institute of Medicine’s recommended 3.7L of water per day (it’s a lot of water). For the last 15 days of the test, I let my thirst guide me – I only drank when I felt thirsty.

So what happened?

First 15 Days: 3.7L of water per day

For the first 15 days, it literally felt like I was drinking water every five minutes. It literally took effort to consume nearly 4 litres of water every single day.

But how did I feel?

Actually, I felt amazing. I definitely felt more energized and alert. My thoughts were much clearer and my body felt healthier (hard to explain the feeling really).

My productivity definitely suffered as I was running to the bathroom anywhere from five to ten times per day. My urine was so transparent that it could be mistaken for water (sorry no pictures included).

Last 15 Days: Obey Your Thirst!

For the last 15 days, I let my thirst be my guide. I only drank when I felt like drinking. If I felt any signs of dehydration, I would drink a glass of water. The amount I drank was different from day to day (as expected) and ranged anywhere from one to two litres.

So how did I feel?

Surprisingly, no different from the first 15 days. I still felt mentally alert. I still felt energized. Of course, my visits to the bathroom decreased by more than 50% and my urine started to darken, but nothing else seemed to change.

The Final Word

Now I know this is a very weak test. It’s possible that the effects of drinking 4L of water in the first 15 days transferred to the last 15 days. But I did my best to keep all other variables (exercise, food consumption, my environment) as consistent as possible to ensure any noted differences were dictated by the change in water consumption.

So how can you use all of this information? 

There definitely seem to be a lot of opposing studies and ideas on the consumption of water (seems to be a common theme in the field of nutrition).

We all know that water is vital for optimal body function.

But it’s important to understand that it’s possible that your current drinking habits might be dictated by the slogans crafted by large bottled water corporations rather than your own body signals.

It’s important to understand that there is such a thing as too much water and that constant excess consumption can put a lot of stress on the kidneys. It’s important to understand that a good fifth of your overall fluid consumption comes from your (solid) food.

So how much water should you drink a day?

In my opinion, and based on the little test I conducted, you should let your thirst be your guide. Your body is an incredible machine. Maybe it’s best that we let it make these kinds of decisions for us.

What are your thoughts on water consumption? Please share them in the comments below. I’d love to know what you think.

27 thoughts on “How Much Water Should I Drink a Day? The Truth Behind Water Consumption”

  1. I find it pretty awesome you decided to test this for yourself.

    The only problem is there really isn’t anyway to know for sure how much water you were getting throughout the 30 days. As you mentioned before, pretty much everything we consume contains water.

    So even though you were drinking 3.7L of water in the first 15 days, who knows what your real consumption was. The same applies to the final 15 days.

    Regardless, I really dig anyone who is willing to test science for themselves and see what happens. Awesome post!

    1. Hey Robert! I think testing is a really important element that a lot of people overlook. There is so much conflicting information out there (as you can see in this post, for instance) that it’s necessaryto test things out for yourself and see what works and what doesn’t.

      And you’re right – it’s hard to tell how much water I was truly consuming. However, as mentioned, I did try to keep other variables consistent throughout the entire month. So, for instance, I made sure my exercise patterns, weekly eating habits, and overall routine stayed consistent while the only thing that changed was my water consumption. So if I was consuming excess fluid from food, I was doing so both in the first 15 days and the last 15 days. It’s as close as I could get to keeping things consistent.

      Thanks for stopping by!

  2. Hi,

    The 2L of water myth actually came from a German study around 50 years ago that people have jumped on. It concluded that on average 2L is the volume of water we should consume each day. However what isn’t reported is the second half of the statement that says most people will obtain the correct 2L through normal eating and drinking.. not that you need to consume 2 specific litres.

    So I guess this also backs up your findings.. just eat and drink normally for you 🙂

  3. I’m really glad you decided to address this topic. So many bodybuilding and strength training advocates say you should drink a gallon of water per day. That’s really excessive. And many in the general health field are constantly telling us to drink more water.

    Of course water is great, and it’s a mistake not to drink any (some people only drink tea, coffee, beet etc.). But too much of any fluid will put the kidneys under too much stress, and it can be detrimental in other ways as you say. So yes, drink water, but don’t force it down. Drink when thirsty. Great post.

    1. I’m happy you agree David. I think it’s definitely important to try things out for yourself and see what works. Try letting your thirst be your guide for a few weeks and see if there are any differences. You might be surprised at what you find…

  4. Hey Srdjan,

    nice post, interesting stuff! 🙂
    Yeah I think back in the day when folks were eating more natural, they only drank maybe once, twice a day is my guess.

    Or can you imagine a knight with his water bottle ready: “Excuse me sire, we will resume our worthy struggle, but first I must hydrate!”
    Right next to the protein bars…

    Hey every time I see your site it looks different…but cooler every time, too! 🙂


    1. That’s a good way to look at it Mark. Even if you think back to the Paleolithic man, you’ll notice that he didn’t have accessible water at all times. He let his thirst be his guide and only drank when necessary. He seemed to do alright for himself 🙂

      And I’ve recently done some restructuring to improve the loading time of my site. I don’t want all my wonderful readers to have to wait any more than they need to. I’m glad you like it!

  5. Thanks for the great post Srdjan! Glad to see someone looking into the reasons behind how much water we drink…Keep up the great posts!

  6. I do drink a lot and boy do I visit the restroom. At work its about once every 50 minutes. At home I tend to drink less and therefore visit the restroom less. I do wonder how much stress has been placed on my kidneys? I suppose I’ll focus on consuming a little less….just to see if there’s a change for me. Thanks.

    there is a difference for me.

    1. Hey John, I have a friend who drinks up to 5L of water per day. He visits the restroom at the same intervals as you it seems. Any excess fluid will over stress the kidneys (it’s making it work that much harder). Try cutting the consumption down a bit for a week and see if you feel any different. Try letting your thirst be your guide for a while and take notice of changes. Your goal should be to figure out what the right consumption is for you.

  7. Hello Srdjan

    I just read the post and Im not surprise with your results actually I try to drink a lot of water a day but at the same time I try to moderate my consumption due to my own experience, I was at the gym working out like crazy and without realizing I drink up to 3 liters on 2 hrs, let me tell you that it was horrible I couldnt leave the bathroom for at least 30 min and at the same time could feel how my body was feeling weak and dizzy…I had to stop the workout and eat something, since then I recomend not to overdrink water and stay with how much your body tell you to drink also drinking tons of water is as bad as not drinking any… like you say before…
    thanks you for the info confirmation and its awesome to find someone as passioned for health like I am…

    loking foward for a new post


    1. Hey B, your story goes to show just how important it is to listen to your body. It knows best. Although water is clearly good for you, the saying remains – too much of a good thing eventually becomes a bad thing.

      Thanks for your comment!

  8. This must be the most refreshing read about the topic of water I’ve come across (pun intended).

    I remember reading ‘your body’s many cries for water’ many years ago and experimenting on myself and others. End results were mixed, but I think that the conclusions reached in the book are too simplistic, but only at times.

    Since then I’ve let my thirst be the guide. But I only do this on the basis that I eat real food, and am tuned into my body and its needs pretty well.

    As you alluded to, the problem with blanket recommendations is that they don’t tend to work. I wrote about the problem of generalisations in my recent blog post about fat loss (I’m on my iPhone and dont have the link to hand).

    One recommendation I find that works more often than not is to have a drink of water when you first get up, and let your body be the guide as to the volume. This seems to set people up for the day and gets them tuned into the feelings of thirst, helping them distinguish them from the feelings of hunger.

    Hope this helps someone!
    Keep up the good work,

    1. Thanks for your insights George! Coincidentally enough, I’ve recently started my mornings with a nice glass of water and I’ve been feeling great (maybe it’s all part of this IF testing I’ve been doing).

      I’ll have to check out this book you’re referring to. Who is the author?

  9. My chiropractor has recommended that I drink half my body weight in oz of water daily. I weigh 160 lbs and drink approximately 80 oz of water per day usually with fresh squeezed lemon. He also recommended that if you have a cup of coffee to drink two glasses of water for every cup of coffee that you drink. I have never been a soda fan but not long ago I had a steady daily intake of energy drinks. For the past couple months I have eliminated all drinks from my diet except for fresh juiced vegetables in the morning, my 3 bottles of water (80 oz), a cup of coffee during the day at some point and a couple of beers in the evening. Beer is the next habit that I will reduce.

    Since I have increased my water intake I have felt my muscles more relaxed and have had less tension in my neck, shoulders and back. I don’t contribute all the gains to my water intake however. I have been more active with cardio several times a week and have been stretching daily which I contribute to feeling better.

    – Destin

    1. Destin, it goes to show that we’re all different. Question: what do you think would happen if you stopped drinking so much water? You think you would feel different?

  10. Hi Srdjan,
    Great info on the water topic, we live in a very humid area in the Summertime. So I do drink quite a bit. Only filtered water from the tap though, (tap filter) I refuse to be ripped off with the bottled water with minerals too, mmmmmm, (why)? I’m sure I read somewhere that our kidneys find it hard to deal with minerals in water. Correct me if I’m wrong……..I am inly 5ft. tall and 8stones in weight, so surely I wouldn’t need to drink as much as someone 6ft. 6ins. do I ??????
    All your topics are fab and I have forwarded them on to my Husband, especially the one on strengthening your knees, he has big probs. with his……….
    Cheers, Tania

    1. Hi Tania. Your filtered tap water already contains a number of minerals that your body needs, while mineral water claims to have 4 times the amount. I just don’t know how accurate those claims are. However, I remember reading that there were (possibly) some correlations between mineral water and kidney stones (I’ll have to look more into that to see if it’s actually true). And, yes, your height (and more importantly weight) is a factor in how much water you should be drinking. A heavier person requires more water than a lighter person.

      And thanks for sharing the articles! I really appreciate it 🙂

  11. Oh thank goodness, i have been forcing myself to drink 2L water every day in the hopes of this assisting my weight loss. For me 2L of water may as well be 20L. I really dislike the taste of water. Previously if i drank 1L water per week that was a lot. I have tapered down recently but i was always fighting with myself for not drinking the 2L water per day. Now at least i can set my mind at ease and drink when i am thirsty. Instead of having tea/coffee now when thirsty i have water instead. I only allow myself 1 cup of coffee if i have had at least 1 L water. Thank you so much for this insight!

    1. Michelle, your approach is great. Allowing yourself a cup of coffee if you’ve had 1L of water is the right way to go about it. I always advise to listen to your body. If it says it is thirsty, nourish it with water.

  12. So glad to read this article because I agree with everything you’ve said but can never persuade my friends. I only drink water when I’m thirsty and I avoid drinking cold water. Now I can send your article to my friends and show them the true story of water consumption. Thank you for writing this.

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