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I've always been skeptical about claims that the majority of the human body is actually water.

I've heard and read estimates that anywhere between 55% to 70% of the human body is water. Which I take to be H2O.

So are humans mostly made out of water? If so, in what measurement and what is defined as the 'human body'?

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    You might try this on the Biology site. But since the answer most likely can be found in any high school biology text, you may not get much of an answer. But consider a steak vs beef jerky :-) – jamesqf Feb 16 '17 at 20:02
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    As a bit of further elucidation... Water in the body need not be "free" water - that is, water that is free to move around within its local area (like inside a cell or in the bladder). Water quite often bonds with other molecules. Such chemicals are referred to as Hydrates. Such water would still be included as water in the body, as hydrates can generally gain or lose water relatively easily (as the bonding is not intramolecular in nature). – Glen O Feb 17 '17 at 15:56
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    We are Ugly Bags Of Mostly Water. – Shadur Feb 17 '17 at 22:36
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According to Human Body Composition:

The percentage of body weight as water varies from 70% to 75% at birth to less than 40% in obese adults.

  • So in weight, that awnsers part of my question. Is the water h20? As in one part oxygen 2 parts hydrogen. – TheJulyPlot Feb 16 '17 at 20:09
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    @TheJulyPlot yes, definitely H2O. 57% of the water is within individual cells and 43% is outside individual cells. – DavePhD Feb 16 '17 at 20:17
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    @iamnotmaynard fat tissue is only 10% water, less than bone. – DavePhD Feb 16 '17 at 20:44
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    @TheJulyPlot The 43% can be broken down as: 7% of the water is in the blood stream as plasma. 4% is excretory fluids. 20% is in the lymphatic system. 7% in bone and 7% in connective tissue. According to table 3.1 and pages 35-36 of the reference. – DavePhD Feb 16 '17 at 21:26
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    @TheJulyPlot: Yes, water is H20. There's no other kind of water. – jamesqf Feb 17 '17 at 5:37
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On what grounds do you base your skepticism about thus issue? There is all the necessary scientific literature available to support the following view:

  • On average, the body of an adult human being contains 60% water. Most of the water in the human body is contained inside our cells. In fact, our billions of cells must have water to live. The total amount of water in our body is found in three main locations: within our cells (two-thirds of the water), in the space between our cells and in our blood (one-third of the water). For example, a 70-kg man is made up of about 42L of total water.

(www.nestle-waters.com) enter image description here

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    Can you link to the page this quote was taken from? – iamnotmaynard Feb 16 '17 at 21:16
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    I'm not sure that's a particularly trustworthy source since it exists for the purpose of selling bottled water. – Kaithar Feb 17 '17 at 12:10
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    @Kaithar - that's a skeptical comment, but can you prove that what they say is not true? – Joe Feb 17 '17 at 12:12
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    @Joe based on the source provided from the other answer... Blood plasma is 7% of the body's water with the remaining blood related water being cellular, so that bit of the source seems dubious. It's silently factoring in body fat, since it doesn't mention fat but without fat the body is closer to 73% water. Mainly I'm skeptical because bottled water companies have a financial interest in over playing the body's hydration requirements... They profit if they convince people to drink more water than the body actually needs to be healthy. – Kaithar Feb 17 '17 at 12:33
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    @Kaithar if anything a statement by a company like Nestle can be trusted to be true about things like this. Under European laws advertising can't lie. It can withhold information of course, it can overemphasise the importance of things, it can oversimplify, but it can't tell the human body is 60% water when in fact it's something completely different like 10%. – jwenting May 29 '17 at 8:28

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