# The Naked Scientists Forum

### Author Topic: Will I ever drink the same water twice?  (Read 5967 times)

#### bananaboy

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##### Will I ever drink the same water twice?
« on: 02/02/2015 01:19:59 »
(Sorry if this is in the incorrect section, it's my first post)
Just read an article about how likely it is the water we consume was once in a dinosaur!  [:0]
This made me think - how likely is it I'll drink the same water molecule, as I have before?
Just how long does the water cycle take?
Food, fruit, soda - all contain some amount of water, so the probability is surely quite high...
It's all quite odd to me, but just curious!
Thanks

#### chiralSPO

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##### Re: Will I ever drink the same water twice?
« Reply #1 on: 02/02/2015 02:46:31 »
I'm sure there are a few water molecules you have consumed more than once, but it's actually very rare (unless you have been on a space station, where the water is recycled on a much shorter cycle). A typical glass of water has about 1025 water molecules in it (that's 10000000000000000000000000!) So just think how many there are in the whole world.

I don't know how long the "water cycle" is because there are many, many different paths/cycles it can go through.

There is also a difficulty in defining the "same" water molecule. One water molecule has two hydrogen atoms and one oxygen atom, but the hydrogen atoms are always swapping from one molecule to another. If one only counts the exact same three atoms being together as "the same water molecule" then each molecule has a very short life span, and is practically guaranteed never to exist again.

So how am I sure that you have consumed at least one water molecule (the exact same one, with the same three atoms) more than once? Back-wash. Some water that you tried swallowing but ended up back in your glass, only to be consumed again very shortly thereafter. This might be a cop-out answer, but I think otherwise, there is no way you would come across the exact same water molecule ever again.

What do the others say?

#### bananaboy

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##### Re: Will I ever drink the same water twice?
« Reply #2 on: 02/02/2015 03:04:08 »
That's pretty crazy... Surely eventually when I'm a 90 year old man shuffling about I would have unintentionally consumed a water molecule I had once before? (There should be a probability & stats section for these kinds of things!)
I realise it's an odd thought to dwell on, just a curious soul

#### syhprum

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##### Re: Will I ever drink the same water twice?
« Reply #3 on: 02/02/2015 11:24:01 »
It is news to me that water molecules are unstable but if I consumed 10^25 molecules of water allowed it to pass thru my system then re consumed it I cannot believe that not one molecule would remain unchanged .
this is an unlikely scenario if after I had passed thru me it went into the wider environment the chances of me getting it back would be zero.
I would be interested to know what is the half life of a water molecule before it changes ?

#### chiralSPO

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##### Re: Will I ever drink the same water twice?
« Reply #4 on: 02/02/2015 15:11:03 »
The rate of proton exchange in water is highly temperature and pH dependent. However, at room temperature and neutral pH, it has been shown experimentally (by 1H NMR studies of exchange between H2O and D2O) that water molecules exchange protons at a rate of approximately 1000–10000 times per second.

#### bananaboy

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##### Re: Will I ever drink the same water twice?
« Reply #5 on: 02/02/2015 16:31:23 »
All very interesting - water is one of those marvellous things
So, the general consensus the likelihood in reality is very low? (Excluding backwash, sweat, tears etc.)

#### SorryDnoodle

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##### Re: Will I ever drink the same water twice?
« Reply #6 on: 02/02/2015 17:17:04 »
All very interesting - water is one of those marvellous things
So, the general consensus the likelihood in reality is very low? (Excluding backwash, sweat, tears etc.)

Very true, but if you count ingesting the same atoms, then it is most likely you have consumed the same.

On a side note, it is a high possibility that with every breath you take you are breathing some of the same molecules of air that Einstein breathed in. And I find that very.. Not sure what word to use but I get a warm nice feeling from it, although it also means we are breathing what Hitler and Stalin did aswell, but I try and ignore that part.

Overall I think science can be very poetic and reassuring and just bluntly put: amazing.

#### bananaboy

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##### Re: Will I ever drink the same water twice?
« Reply #7 on: 04/02/2015 06:00:18 »
Never thought of that too!
Almost incomprehensible, but as you said quite poetic...
Anyone any other thoughts on this topic?
Thanks

#### Ophiolite

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##### Re: Will I ever drink the same water twice?
« Reply #8 on: 04/02/2015 07:52:36 »
The rate of proton exchange in water is highly temperature and pH dependent. However, at room temperature and neutral pH, it has been shown experimentally (by 1H NMR studies of exchange between H2O and D2O) that water molecules exchange protons at a rate of approximately 1000–10000 times per second.
Could you provide a citation for this please.

#### RD

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##### Re: Will I ever drink the same water twice?
« Reply #9 on: 04/02/2015 10:58:17 »
... quite poetic...
Anyone any other thoughts on this topic?

You're far more likely to be consuming water-molecules that have been in a dinosaur's bladder than in Einstein's.

Quote from: Ilse Cleeves, University of Michigan astronomer
... a significant fraction of water on Earth predates the sun and the solar system ...
http://www.latimes.com/science/sciencenow/la-sci-sn-old-water-on-earth-20140923-story.html
« Last Edit: 04/02/2015 11:12:22 by RD »

#### Don_1

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##### Re: Will I ever drink the same water twice?
« Reply #10 on: 04/02/2015 11:36:16 »

........ A typical glass of water has about 1025 water molecules in it (that's 10000000000000000000000000!)

...... at room temperature and neutral pH, it has been shown experimentally (by 1H NMR studies of exchange between H2O and D2O) that water molecules exchange protons at a rate of approximately 1000–10000 times per second.

Given the above and couple it with the exchange of electrons between the hydrogen and oxygen atoms (not to mention the exchange of electrons between those and other atoms when they get torn away from each other by bio-chemical processes to form ammonia, nitric acid, gastric fluid, urine etc etc) I should think the chances are that no molecule of water present today has ever existed before.

#### chiralSPO

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##### Re: Will I ever drink the same water twice?
« Reply #11 on: 04/02/2015 13:28:17 »
The rate of proton exchange in water is highly temperature and pH dependent. However, at room temperature and neutral pH, it has been shown experimentally (by 1H NMR studies of exchange between H2O and D2O) that water molecules exchange protons at a rate of approximately 1000–10000 times per second.
Could you provide a citation for this please.

I found it in here (Phys. Chem. Chem. Phys., 2002, 4, 2994), but this paper deals almost entirely with proton exchange in solutions of water in dioxane or nitromethane. They cite this paper (S. Meiboom, J. Chem. Phys., 1961, 34, 375) in discussions of proton exchange in pure water.

#### chiralSPO

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##### Re: Will I ever drink the same water twice?
« Reply #12 on: 04/02/2015 13:32:08 »

........ A typical glass of water has about 1025 water molecules in it (that's 10000000000000000000000000!)

...... at room temperature and neutral pH, it has been shown experimentally (by 1H NMR studies of exchange between H2O and D2O) that water molecules exchange protons at a rate of approximately 1000–10000 times per second.

Given the above and couple it with the exchange of electrons between the hydrogen and oxygen atoms (not to mention the exchange of electrons between those and other atoms when they get torn away from each other by bio-chemical processes to form ammonia, nitric acid, gastric fluid, urine etc etc) I should think the chances are that no molecule of water present today has ever existed before.

I agree that the chances are very very small for the same three atoms to come together again after separating for any substantial amount of time. Hence I suggest that only in cases of re-ingesting recently expelled water would the same molecule be involved. Most of them would have exchanged protons by re-ingestion time, but with such a huge sample size, I bet there are a handful of molecules that either did not exchange, or reconstituted before re-ingestion.

I am defining the molecule only by the three nuclei contained in it. If we accounted for electrons as well, I'm really not sure how one would define "same."

#### evan_au

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##### Re: Will I ever drink the same water twice?
« Reply #13 on: 04/02/2015 17:28:07 »
Quote
If we accounted for electrons as well, I'm really not sure how one would define "same."

It is hypothesized that every electron is absolutely identical to every other electron in the universe, so it is almost impossible to distinguish two electrons. (You can do some tricks with unpaired electrons of an isolated atom, but that is not much use outside a quantum computer.)

A similar statement could be made about protons, neutrons, hydrogen nuclei or oxygen nuclei, so it is almost impossible to distinguish two nuclei. (You could do some tricks with nuclei in an excited state, but that is not much use outside a sensitive mass spectrometer.)

Oxygen has only 3 stable isotopes (the others all last < 2 minutes): 16O makes up 99.74%
Hydrogen has only 2 stable isotopes: 1H makes up 99.989%. (The half life of Tritium is 12 years)

So almost all the water in the world will be composed of 16O and 1H, and these are the most likely atoms to be re-ingested after passing into the ecosystem. You can estimate the probability of reingesting a particular atom, but you can't physically tell that it is the same atom.

#### SorryDnoodle

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##### Re: Will I ever drink the same water twice?
« Reply #14 on: 04/02/2015 23:56:56 »
but you can't physically tell that it is the same atom.

Yeah, probably not, but it is just one of those interesting facts that we breath the same air as historic figures and that maybe we drink the exact same atoms and maybe even a molecule or two of water a couple of times during our brief visit to the wonderful and terrible earth.

As I said earlier, I think science can be very poetic and this is one of those topics that are just for the heck of it.
I would like to think that it is not only religion is allowed to use the word spiritual, I would apply it to these types of thoughts and discussion, but that is just my personal view.

#### jccc

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##### Re: Will I ever drink the same water twice?
« Reply #15 on: 05/02/2015 00:59:25 »
You can drink the same water easily. Collect pee and distill it.

Some Japanese do that without distill.

#### The Naked Scientists Forum

##### Re: Will I ever drink the same water twice?
« Reply #15 on: 05/02/2015 00:59:25 »