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How much should you drink each day?

Last updated: January 10, 2021
(5 min read)

If you read this, you probably already heard how beneficial staying hydrated can be (if not, you can read more about it here). So let's get a bit technical and explore how much water you should target to drink.

Your body consists of around 60-70% water. Every single cell in your body needs it to function. It helps to regulate your temperature, lubricates your joints, and helps you to flush out toxins. Because water is involved in so many functions, you continuously lose some of it. How much, you ask? Well, quite a bit. Most people are surprised just how much. According to the U.S. National Academies of Sciences, Engineering, and Medicine we need on average: - About 15.5 cups (3.7 liters) of fluids a day for men - About 11.5 cups (2.7 liters) of fluids a day for women

If these figures seem pretty high, you are right. Because there is more to them. First of all, they are highly aggregated averages. A 120 kg bodybuilder has very fluid different requirements than a 60kg software engineer. Also, as you may already have heard or guessed, we don't need to drink all our fluids. But before we get there, let's start to take a look at how you can find out how much you (yes, you, reading this) need individually, starting from the top.

Your weight

This will probably not come as a surprise, but yes, the more you weigh, the more water your body needs. This is also the main driver why men (on average) need more fluids than women. Except when taking special requirements like pregnancy or breast-feeding into account, women need roughly as many fluids as men. But men simply weigh more on average. This also immediately makes it evident that while the above-recommended figures are a decent place to start, they might not apply to you.

Physical activity

The second most important factor (for most people) is your physical activity. It makes a big difference whether you are mostly sitting at a desk or are highly active throughout the day. The more active you are, the more you sweat and breathe, both of which will reduce your fluids. On average, you lose around 3.5 - 5 cups (0.8 - 1.2 liters) through sweat when exercising (however, for high-performance athletes, this figure can be up to three times as high!).

Climate and other environmental factors

Finally, there is the environment. It's probably the most complicated factor because it depends on various aspects, including how well you are accustomed to the environment. To understand this, we need to look at the purpose of sweat. Sweat is used to cool the body. The hotter it gets, the more we will sweat. But contrary to what most people think, we will sweat more the better we are accustomed to the heat (to optimize the cooling effect). Humidity also plays an important role. Sweat is able to cool us only when it evaporates. The higher the ambient humidity gets, the less sweat evaporates. To compensate for that effect, we need to sweat more. If by now you feel slightly confused, don't worry. For most people, the climate is probably the least important factor. In fact, if you spend most of your time indoors in moderate temperatures, you can safely ignore it.

Special factors

So far, we have looked at general factors that apply to everyone. To be precise, there are additional factors that can play a role. These include pregnancy/breast-feeding as well as various illnesses. To get into the detail would be out of this article's scope and better left for a dedicated discussion with a physician of your trust.

Fluid requirements vs. how much you need to drink

While we have not talked about specific formulas to calculate your intake (we'll get to that later), we covered the most important factors that determine your fluid intake. But, as we established before, fluid requirements don't equal how much you need to drink. The main reason is that you get around 20-30% of our required fluid from foods. Not only from the water inside the foods you eat but also from a process called metabolic oxidation, which essentially creates water from other macronutrients.

Can I rely on thirst?

Reading all this might let you wonder "This is all good and well, but it sounds really complicated. Can't I instead just wait until I get thirsty?". It's a great thought, but we recommend against it. Thirst (like pain) is your body's way of telling you about an imbalance. Even worse, based on our modern lifestyles, we trained ourselves to ignore thirst. Your body might try to get water by getting hungry instead (which is harder to ignore), but that can lead to unwanted weight gain. So especially if you want to feel at your best (you can read more here), you should not rely on thirst alone.

Technology to the rescue

While there are various formulas to calculate your optimal intake, we recommend relying on existing calculators instead (this one is pretty good). These will take the various factors into account and give you a recommendation. Or, even better, get a dedicated app to help you understand your individual requirements and also help you track what you drink. Fluid was made precisely for that purpose. It's free to use and (unlike many other free alternatives) does not contain distracting banner ads.

Bonus: Can I drink too much?

Technically, yes. If too much water is consumed, the electrolytes in the blood can become too diluted, and this can cause an array of serious issues. But while this is true, it's probably not something that you should worry about. Our body can generally get rid of excess water through urine. To overwhelm it, you would need to drink a lot. How much? Well, it depends, but under normal conditions (you are not actively exercising and/or in a hot & humid environment), you would need to drink more than a liter (~4 cups) per hour for an extended period of time.

Bonus: Does it matter what I drink?

Not as much as some people might tell you. For example, orange juice contains 90% water. The same applies to sodas. Milk has around 87%. Coffee is 98% water - and recent studies show that it seems to have a much milder diuretic (water loss) effect than previously thought. Once you worry about what you drink, you probably worry too much about it. If you follow the recommendations based on your weight and exercise, you can safely count any non-alcoholic drink as 1:1. The easier you can follow a routine, the more likely you will stick to it. We recommend avoiding the complexity of micro-managing your fluids.

But what about alcoholic drinks? Here, things get a bit tricky. Alcohol can actively dehydrate you (the higher the alcohol content, the stronger the effect). Dehydration is one of the key drivers of a hangover. So no, alcoholic drinks should not count towards your drinking goal. In fact, you should even consider to make up for it. If you want to read more about this, you can head over to Healthline.

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