
Why Can't We Drink Sea Water? - todsul
http://globetrooper.com/notes/why-cant-we-drink-sea-salt-water/
======
jforman
Alas, this article is not remotely accurate. In truth, the best thing that you
can drink when extremely dehydrated is lightly salted, sugared water (on an
empty stomach, at least — food can provide the salt/sugar otherwise). This is
why Pedialyte, which contains both salt and glucose, is often given to
dehydrated children and adults. This is also why Gatorade is better than pure
water.

The reason for this is that water absorption in your small intestines is
significantly more complicated than depicted in the image in this article.
Water is not absorbed across a simple membrane passively — rather, the small
intestine is a two-layer barrier with specific transport proteins positioned
in each layer of the barrier in order to pull nutrients into the body at a
very high efficiency.

A dominant theory right now is that sodium-glucose co-transporters are
responsible for drawing water into the body (see
<http://www.ncbi.nlm.nih.gov/pubmed/16322051> and
[http://en.wikipedia.org/wiki/Sodium-
glucose_transport_protei...](http://en.wikipedia.org/wiki/Sodium-
glucose_transport_proteins)). Specifically, an osmotic gradient is created by
(I think) the Na/K active pump ("active" meaning the body uses up ATP to
overcome the normal steady state). The Na/glucose co-transporter then uses
this gradient to pull those molecules into the body, bringing water with it —
the water of hydration.

If we were hydrated using a simple system such as the one depicted in the
link, we would be orders of magnitude more responsive to the food we eat. Our
bodies are very good at maintaining homeostasis, but it takes a lot of
complexity to do it.

Edit: it's worth noting that seawater may indeed be too highly concentrated to
drink safely, even in moderate quantities, if it's true that the kidney cannot
excrete at a greater concentration of salt as is present in seawater. This
link from Wikipedia suggests this is the case:
<http://www.newton.dep.anl.gov/askasci/bio99/bio99416.htm> . But the posted
article's explanation is entirely off-base in its explanation regardless. And
I'm not even sure what of seawater would be absorbed on an empty
stomach...it's possible more salt than water would be absorbed, leading to
diarrhea as water is left unabsorbed in the intestine, leading to dehydration
from poor water absorption _and_ poor salt excretion.

~~~
ahoyhere
Lots of people have died from drinking sea water. It's still a Very Bad Idea.
Your argument is along the lines of "They got technical details wrong; salt
water is sometimes important; therefore the whole thing is wrong." But that is
like saying the advice to "Do not handle rattlesnakes" doesn't apply because
some folks get a great deal out of handling rattlesnakes. The fact is, people
who don't know what they're doing shouldn't handle rattlesnakes… or drink sea
water.

Now let's talk about oral rehydration salts -- the non-fancy name for the salt
water and "glucose transporters" you described.

The salinity of Oral Rehydration Salts/Solution is nowhere near as high as sea
water -- and without the sugar, saltwater doesn't rehydrate. The formula for
making it yourself is about 1/2 tsp salt in a liter of water, plus 6 tsp of
sugar. That's a lot of sugar to balance out just a little salt: 1:12 ratio.

A quick Google suggests that 35g of salt is what one would expect in a liter
of sea water (on average). A tsp of salt weighs 5.7 g. Therefore, the
concentration of salt in sea water is 6 teaspoons vs 1/2 tsp in ORS, or 12x
the concentration of salt.

And no sugar.

I drink ORS on a regular basis to deal with one of the side effects of chronic
fatigue syndrome: an imbalance of hormones in the body which leads to
insufficient electrolytes which leads to POTS (postural orthostatic
tachycardia syndrome), dizziness, muscle cramps & twitches, brain
fog/inability to think straight, and inability to drink adequate water.

ORS has been a total life changer for me -- before, doctors just said I was
"too out of shape" when sitting up/standing led to a doubled heart rate,
dizziness, the feeling that "the bottom dropped out of my head", near
fainting, etc. Because that's a valid explanation when a 27-year-old nearly
passes out from standing up. (Not.)

Drinking a little salty-sugary solution solves my symptoms in 20 minutes.

But I sure as hell wouldn't drink sea water.

~~~
mikeash
The article is titled, "Why Can’t We Drink Sea Water?" The technical details
that they got wrong are the whole point of the article, and it is completely
reasonable to complain when such an article is inaccurate.

~~~
djacobs
I agree. No correction would've been necessary if the article had been titled
"Don't drink sea water (supported by scientifically inaccurate, but fancy-
sounding facts)".

------
Loic
A French biologist Alain Bombard as proved with a 65 day trip across the
Atlantic that one can drink sea water up to one liter per day if one can drink
raining water and water extracted from fishes too. So, yes, you can drink sea
water, but not too much. So, do not keep in mind that you absolutely cannot,
as it can bring you an extra day of survival (if you do not have other source
of water).

<http://en.wikipedia.org/wiki/Alain_Bombard>

~~~
electromagnetic
Actually if you're dying of dehydration, chances are you're somewhere
exceptionally hot, because it's rare that you wouldn't be able to find water
in 3/4 days in a temperate climate.

If you're in an area where you're perspiring a lot, then occasionally drinking
sea water would actually be beneficial as there aren't many readily available
sources of salt.

I work construction, in the longest heatwave of the summer I was putting
tablespoons of salt into my water jug as it's quite easy to become nauseous
when drinking a gallon of water inside a work day. Not to mention you don't
want to get disorientated or light headed whilst 30ft in the air.

Long time survival in a hot environment requires a source of both fresh water
and salt. The ocean is a far easier source of salt than searching for anything
in nature.

~~~
mynameishere
Wouldn't it be more pleasant to drink fresh water and take salt pills
separately?

~~~
ghshephard
It's difficult for me to drink fresh water in large quantities (more than a
liter an hour) but when I put electrolytes in them, I find I can drink
somewhere on the order of 2x to 3x more.

I buy these 100 at a time - seems to do the job pretty well.

<http://www.hydrationdepot.com/Qwik-Stik.html>

------
carsonbaker
This is controversial, but Alain Bombard
(<http://www.nytimes.com/2005/07/24/obituaries/24bombard.html>) sailed across
the Atlantic, surviving on seawater, fluids from fish, and plankton.

Seems like you might be able to drink a little seawater, but not too much --
maybe a pint a day at the most. Natural History magazine has a great article
on this:

[http://naturalhistorymag.com/picks-from-the-
past/181950/thir...](http://naturalhistorymag.com/picks-from-the-
past/181950/thirst)

------
donw
Although only moderately related to the article, it's worth noting in this
situation that the ocean could still be of use to you in maintaining water
levels.

Arid climates are dangerous because they force us to sweat in order to
maintain body temperature, at a rate between 1L and 2L per hour, depending on
how much you're exerting yourself.

While you can't drink the water, you certainly can use it as a heat sink.
Taking a bath and soaking your clothing in the water will both cool you down
and assist in the same evaporative cooling process, reducing the amount you
need to sweat.

Coupling extra evaporative cooling with limited movement during the day will
help you conserve a lot of water, and could extend your survival time by more
than 50%.

------
iqster
I have to recommend a cool book on this ... Why Geese Don't Get Obese. It
delves into the biological systems of different animals and explains how they
do some amazing things. For instance, there was a chapter on how fresh water
fish and salt water fish differ in how they drink water.

~~~
mechanical_fish
Thanks, I was just wishing that this article would have gone into that.

Presumably whales and other marine mammals _can_ drink ocean water -- how else
would that work? -- so it's not an inevitable design constraint that our
internal salinity is less than that of the ocean. Presumably our ancestors
evolved to drink low-salinity water (and eat separate sources of salts, and
automatically mix the correct salts into the water in the correct proportions,
and maintain those proportions at all costs -- lots of overhead!) because
fresh water is what's plentiful in our habitat. In other words, it's because
lakes, rivers, and springs yield fresh water that we've evolved all these
mechanisms for tolerating fresh water.

Another nice poetic question is: _why_ are we made of so much water? The
answer is that life evolved in the ocean. We're built out of crucial parts
that were developed in the ocean and that can't operate outside of a saltwater
environment. So life colonized the land by evolving a way to carry its own
ocean with it. ;) I'm a giant EVA unit for ocean-dwelling cells!

------
dpcan
This is an article about why we can't drink salt water :)

On hn I usually expect these titles to be tongue in cheek and the article to
be about an invention that would allow us to inexpensively purify sea water
for drinking.

Speaking of which, IS there such a device? If not, why not?

~~~
acangiano
<http://www.thewatercone.com/Index.html>

~~~
ChuckMcM
That is so cool. We built solar stills in scouts but this one seems really
practical.

------
russell
Reverse osmosis is getting to be a viable water purification method even if
you are not an energy rich middle eastern oil producer. Back in the 90s I
lived in a community of about 160 homes in the mountains above Woodside CA. We
had our own mutual water district. We had good water quality, but were
pestered by the county to upgrade our treatment facility because our reservoir
was subject to contamination. There was a gas station with leaking tanks about
50 feet from the edge. We finally installed a reverse osmosis filtration
system, not to create fresh water from salty, but to remove any possible
contaminants.

The town where I now live is planning to install a desalinization plant
because the main water source was contaminated by MTBE contamination from the
Chevron station. It is being held up by an over zealous coastal commission.

~~~
Retric
Reverse osmosis takes more energy the more polluted the source is, because
osmotic pressure increases based on the relative concentrations on either side
of the semi permeable membrane. So don't confuse the costs of filtering
contaminated fresh water with sea waster.

------
anateus
If you have only a smaller amount of fresh water, it is possible to survive
with little ill effects if you mix fresh and salt water in a 2:3 ratio
(respectively).

[http://en.wikipedia.org/wiki/Seawater#Human_consumption_of_s...](http://en.wikipedia.org/wiki/Seawater#Human_consumption_of_seawater)

------
iwwr
Kidneys like marine mammals have could help us.

Relevant: [http://www.scientificamerican.com/article.cfm?id=how-can-
sea...](http://www.scientificamerican.com/article.cfm?id=how-can-sea-mammals-
drink)

------
philfreo
> When we drink too much _fresh water_ , excessive water passes into our cells
> to try to regulate the concentration (which can become futile)... If they
> absorb too much water, the cells will swell and burst, which can lead to a
> quick death

I've been scared of this since I was a kid, and nobody ever told me how much
water was too much.

~~~
superted
I drank something between 4-6 liters of water in a couple of hours time last
summer, and ended up with fever and throwing up excessively for the remainder
of the day. I was more or less knocked-out for the next couple of days. So I
can definitely tell you that drinking too much fresh water in a short time
frame is anything but healthy...

~~~
acangiano
Your kidneys can only excrete 1L/hr under optimal conditions. So you were a
victim of water intoxication, but were very lucky you didn't die. People died
for drinking much less water than you did.

~~~
dhughes
Being in poor physical shape probably had more to do it.

People drink litres of pop at a sitting too without much effect on them other
than being obese.

~~~
mturmon
Read up on water intoxication deaths of marathoners and discover why your
simple idea is wrong.

~~~
dhughes
I did I went to Mayo Clinic and NIH websites and the gist of it is too much
water results in rapid loss of sodium and your body's cells swell up with
excess water.

Drinking litres of pop such as low sodium would also be dangerous according to
the descriptions given at those sites, so many people these days just drink
pop and lots of it.

Any on-going health problems such as poor health in a person would increase
the risk of a serious condition such as water intoxication.

It's probably why there is some sodium in bottled water.

------
S_A_P
I saw an episode of "Good Eats" that Alton Brown discussed this. He stated
that an 8:1 ration of fresh - sea water could be used to extend water supplies
as well as make your body retain the water longer so less is needed vs pure
water. I would be curious to know if this is a good ratio, should I ever
become shipwrecked :)

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kragen
[http://www.straightdope.com/columns/read/2131/what-would-
hap...](http://www.straightdope.com/columns/read/2131/what-would-happen-to-
you-if-you-drank-seawater) has somewhat more in-depth and better information
on the topic. This article is disappointing.

------
abeh
A university biology professor mentioned in a lecture that a small percentage
of people have kidneys strong enough to drink sea water.

------
zokier
But why cells are so finicky about salinity? Why can't cells operate properly
with some salt present?

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error
it's very salty :)

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dbbo
Maybe I'm just biased because of my curriculum, but I didn't find this article
informative at all. I actually found it overly dumbed-down. Perhaps it was
meant for people with zero biology/chemistry knowledge.

------
klbarry
I'm surprised I was never taught this before. Great post.

