Would a sea water enema help hydration?

05 December 2010


Dr Chris,

I hope the subject might get your attention but I guess as a Doc....!

Question..as a matter of survival and in dire need of fluids without potable drinking water would an anal infusion of sea water work?  If it would how much fits down there, a glass, a litre?

I know of an occurrence where brackish water was administered that way to avoid the stomach upset and consequent problems drinking it would have resulted in.

Great show, Dave's kitchen science gets my vote.


John Burgess


We put this to Miles Parks, Gastroenterologist, and Ari Ercole, Intensivist, both from Addenbrookes Hospital...

Miles - Using the rectum as a means of administering fluid replacement in dehydrated individuals is an interesting idea. The colon or large bowel functions primarily to absorb fluid, normally doing so of course as material enters to the caecum from the small intestine, the material which has not been digested, fibrous products and so on, together with a substantial amount of fluid and solute enters into the colon, and the fluid is then sucked out as the material goes around the 4 feet or so of the colon to form up the stool.

And so, you can see the colon is well designed for absorbing liquid but it really needs to do so in the context also of transport of solute, that's to say of sodium and chloride ions, and so on. It's the absorption of these, of the solute itself, which then creates the osmotic gradient which sucks fluid across the lining of the bowel, and into the bloodstream.

So, bearing these things in mind, I do think that water enemas on their own, or water on its own, is perhaps unlikely to be absorbed in a clinically significant quantities, and of course, it's just likely to come out of the rectum again whereas, I think administering saline or something of that type would potentially lead to quite a significant absorption of fluid.

Diana - Water on its own probably wouldn't do very much, but a saline solution could give one a better chance of a drink. But what if you're stuck for saline drips and all you've got is a much saltier seawater?

Ari - Unfortunately, giving yourself a seawater enema for hydration if you've had the misfortune to be stranded at sea is a complete thermodynamic nonstarter.

The problem is that the salt in seawater is much more concentrated than the concentration of all the various solutes found in body tissues. Since, to a first approximation at least, the gut can be thought of as a sort of semipermeable membrane, this will lead to water molecules tending to move from the body through the gut wall, and into the seawater to reduce the concentration difference. This process where water moves along its own concentration gradient across a semipermeable membrane is called osmosis, and it's very important in biology. In this case it will actually result in you becoming increasingly dehydrated.

The situation is reversed with freshwater which would be successfully absorbed. Having said that, neither procedure would be very safe especially if the water was dirty.

So, giving yourself a seawater enema if you're trapped at sea is likely to make you lose water.

Of course, giving yourself a seawater enema if you're trapped at a cocktail party is likely to make you lose friends as well!


The above discussion is completely wrong and somewhat shocking coming from MD's. The colon transfers water by active transport of NA+ ions.. In normal digestion by the time our digestive effluent reaches the colon it is hyper-tonic. The cells lining the colon first pump sodium into their capillaries and the water follows. The cells then pump the sodium out. A salt water enema with sodium chloride would allow the colon to net absorb iso-tonic water. That is what the colon does; it grabs water from a hyper-tonic solution.

Have you got a reference you can refer us to for the active transport of water from the colon please?

It was reported that seamen adrift for a month survived by rigging up a sea water enema. Dr Mark Pimentel, gastroenterologist feels that this would work because of the colon's function to absorb water.
Administering enemas in the early part of the last century were quite common and a means of administering medications. A favorite Rx for migraine was the coffee enema - because of the stomach sensitivity that was associated with vomiting.
As a scuba diver and medic I feel it is important to decide if this is a feasable method. Should be an easy experiment to conduct. I am thinking of the many lives that could be saved. If anyone has experience of information please contact me at the grossan institute. Thanks

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