# could you really filter saltwater via your rectum? **URL:** \ **Category:** Factual Questions\ **Created:** [January 22, 2011, 7:54am UTC](https://boards.straightdope.com/t/could-you-really-filter-saltwater-via-your-rectum/568547 "2011-01-22T07:54:22Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [January 25, 2011, 3:24pm UTC](https://boards.straightdope.com/t/could-you-really-filter-saltwater-via-your-rectum/568547/21 "2011-01-25T15:24:09Z")
**Blake** , you are indeed correct that far more water is absorbed in the small intestine than in the colon. I had thought the ratio was about 25% small bowel, 75% colon while in fact it is more like 90/10%. So thanks for the correction. (Less than 2% of water gets absorbed in the stomach; alcohol is somewhat better absorbed there). As a side note, the large colon is not real good at secreting water. Colonic distension does trigger some secretion of fluids to try to correct the distension, but in most folks it’s not a large amount. Hence the problems of chronic constipation. Reabsorbtion is chiefly what the colon does with water. ---
**Author:** ![paddo](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@paddo](https://boards.straightdope.com/u/paddo)\ **Post date:** [December 15, 2012, 1:35am UTC](https://boards.straightdope.com/t/could-you-really-filter-saltwater-via-your-rectum/568547/22 "2012-12-15T01:35:36Z")
Someone years ago told me about a book he read by a seasoned mariner. He said that due to the characteristics of the kidney (its ability to remove salt from the blood, obviously inferior to sea animals), it is nevertheless possible to live on sea water but only if you are never at all dehydrated and drink very large amounts of seawater multiple times a day. I don’t know the details of how much and how often - probably just about as much and as often as you can stand I would guess. Once you get to a small level of dehydration it’s too late, your kidneys can’t recover the situation and you will die without fresh water. He even went out on a small boat for 2 weeks drinking ony seawater to test his theory and said it worked. I wish I knew who it was, I suppose it would be easy enough to find the relevant number(s) that describe the kidney’s characteristics and maybe figure out what he was talking about. Maybe sea water is slightly less concentrated than the salt concentration the kidney is capable of producing? I haven’t really thought about the theory much. On the debate about colon water absorption, if we are to believe the textbook quotation someone posted it states 8l is secreted, 10 l passes throgh and 1 l is absorbed by the LI/colon. That suggests that 50% is absorbed by the LI/colon so the debate may be a draw. but the OP only talks about the colon so taht’s a bit different. ---
**Author:** ![stuyguy](https://avatars.discourse-cdn.com/v4/letter/s/ec9cab/32.png) [@stuyguy](https://boards.straightdope.com/u/stuyguy)\ **Post date:** [December 15, 2012, 5:40am UTC](https://boards.straightdope.com/t/could-you-really-filter-saltwater-via-your-rectum/568547/23 "2012-12-15T05:40:59Z")
> [@paddo](#): > > Someone years ago told me about a book he read by a seasoned mariner. He said that due to the characteristics of the kidney (its ability to remove salt from the blood, obviously inferior to sea animals), it is nevertheless possible to live on sea water but only if you are never at all dehydrated and drink very large amounts of seawater multiple times a day. I don’t know the details of how much and how often - probably just about as much and as often as you can stand I would guess. Once you get to a small level of dehydration it’s too late, your kidneys can’t recover the situation and you will die without fresh water. I have a book titled _ **Survival: How to Prevail in Hostile Environments** _ by Xavier Maniguet that agrees with this theory and argues in favor of drinking modest amounts of salt water in a survival crisis. (Perhaps it is the very book your friend was talking about.) The book features two charts. One shows a person’s degree of dehydration without drinking any water over a period of days. The other shows the degree of dehydration resulting from drinking small amounts of salt water. _Both_ charts predict that a person would die around Day 10. But the while the non-drinker declines steadily over time, losing consciousness at Day 4, the salt-water drinker remains fully functional until Day 7; then he crashes, losing consciousness too, and eventually giving up the ghost. But during those functional seven days, the author argues, the salt-water drinker can do a far better job of securing fresh water sources that will save his life in the long term. ---
**Author:** ![grude](https://avatars.discourse-cdn.com/v4/letter/g/e47774/32.png) [@grude](https://boards.straightdope.com/u/grude)\ **Post date:** [December 15, 2012, 5:59am UTC](https://boards.straightdope.com/t/could-you-really-filter-saltwater-via-your-rectum/568547/24 "2012-12-15T05:59:03Z")
> [@Blake](#): > > There is certainly no justification in the claim that “The colon is primarily responsible for absorbing fluids” > > You can reason this out for yourself if you think about it for a few seconds. > > In a healthy person, ingested material takes several \*hours \*to reach the colon. > > When you are thirsty and drink, how long does it take before the thirst is quenched? Is it 6 hours, or is it closer to 6 minutes? Heck, if you drink excessively following dehydration, how long is it before you urinate? Minutes or hours? That was exactly what I was going to post, hell forget the water what about alcohol or other drugs? Clearly most(not all) are being absorbed before reaching the colon. ---
**Author:** ![Koxinga](https://avatars.discourse-cdn.com/v4/letter/k/4af34b/32.png) [@Koxinga](https://boards.straightdope.com/u/Koxinga)\ **Post date:** [December 15, 2012, 6:32am UTC](https://boards.straightdope.com/t/could-you-really-filter-saltwater-via-your-rectum/568547/25 "2012-12-15T06:32:27Z")
> [@Qadgop\_the\_Mercotan](#): > > And the OP has already been adequately answered by previous posters. No, you can’t filter saltwater (or toxins) through your rectum. So you assert that on the contrary, it would’ve nearly killed 'em? [Previous page](https://boards.straightdope.com/t/could-you-really-filter-saltwater-via-your-rectum/568547.md?page=1)