By Merfolk or mere-people I mean sapient beings who share have some physical traits with terrestrial humans (a humanoid upper body and opposable thumbs at least, if that's not specific enough), live in underwater communities, use tools to some degree (one can likely rule out fire), and have a culture, if not necessarily a civilized one.

This isn't to ask how a merperson expels bodily waste, more how do they dispose of it and avoid it floating all around them?

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    $\begingroup$ In comparison, what do social marine mammals do? $\endgroup$
    – JDługosz
    Jun 2, 2016 at 2:35
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    $\begingroup$ When dealing with the sea, the answer to pollution is dilution. They would deal with it like we deal with farts and burps. In other words: be discrete and preferably do it in a place where you do not discomfort others. $\endgroup$
    – MichaelK
    Jun 2, 2016 at 5:57
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    $\begingroup$ I vaguely remember a short story about a sapient aquatic species living in a stream. Their cultured had a strict hierarchy where higher casts lived upstream. $\endgroup$
    – Guran
    Jun 2, 2016 at 7:51
  • $\begingroup$ From years of keeping fish: Their poop sinks to the bottom, it doesn't float. $\endgroup$ Oct 8, 2020 at 16:32
  • $\begingroup$ @DarkMalthorp- even so, if the merpeople live on the ocean floor it could still be a problem. $\endgroup$ Nov 6, 2020 at 4:17

3 Answers 3


I'm not going to assume a level of technology here, and instead list a few primitive methods that may lay the foundation for later development in your species.

These methods attempt to localize any grossness to one area of the body, where it could be cleaned with some seaweed or something.

Option one: The Three Seashells

Well, one seashell. A big one.

Providing that your merfolk have all of their relevant orifices located closely together, when mer-nature mer-calls, your merfolk might try to find a large, empty gastropod shell to press up against their body and expel their waste into. When they are done, they quickly cap it with something (another seashell?) and then bury it.

The future: Manufactured waste containers are readily available anywhere in society, along with a nearby receptacle for disposing of them.

Option two: Pissing into the Wind

Let's say your oceans have strong currents. A merperson could park themselves right on the edge of such a current, allowing their waste to be moved downstream with it. It would spread out eventually, but hopefully not before going a significant distance from the merperson. This has the added benefit of the running water cleaning them off.

The future: Basically just a space toilet. We probably should have looked at zero gravity solutions first! Your society builds plumbing networks that allow high-strength vortexes to be created at the endpoints. Then, it's easy to build toilets that suck away waste continuously while active. The pipe that refills the toilets could have a receptacle near the endpoint for disinfectant containers that clean off the merperson when they press a button. This water would then also be slurped up by the system. This is probably the cleanest solution.

I made this a numbered list because I anticipated having a third idea, but then I didn't. If I come up with a third unique solution, I'll add it.

  • $\begingroup$ A mer-great answer here, +1 $\endgroup$ Jul 27, 2016 at 12:30

Consider that a creature which is constantly surrounded by water is not likely to have trouble staying hydrated. You might work their necessary anatomy such that they do not ingest or expel liquids.

Instead, all internal waste products get dried and compacted into heavier than water nuggets which upon expulsion, sink into the depths where no MerFolk ever go. Nature tends to solve these kinds of problems for itself.

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    $\begingroup$ Staying hydrated: depends on whether salt or fresh water, as the osmatic pressure is the opposite. Seawater dehydrates fish/anphibians, which have to take in water to compensate. And mammals don't lose fluid that way, but have a very big problem finding drinkable water in the middle of the sea! They won't waste it. $\endgroup$
    – JDługosz
    Jun 2, 2016 at 2:38

My observations of many higher-living land animals (birds, spiders, even monkeys) is that they do not have much concern for toilet habits: they just do it and let it drop out of their living space. Fish and other aquatic organisms very much the same, although in their case they depend on dilution and filtering by symbiotic organisms (if unknown to you, you may want to read up on aquaponics, a system to raise both fish as a protein source, in tanks, and circulate their water through plant crops for removal of their nitrogen-rich waste, which incidentally also is a very good nutrient/fertilizer for the (edible) plant crops).

Of course, many surface dwelling social animals are known to create communal toilet areas or dung middens (quolls, hyraxes, some antelope species, rhinos, even modern humans on the conceptual level at least). But it is not a universal trait (one can argue that humans and monkeys are pretty close, evolution-wise).

I would expect that merfolk would start out just like fish. Once they developed culture and society to the level that their increased numbers caused problems in the health department, they would develop some cultural solutions to the problem, e.g.

  1. not releasing waste upstream from someone else (as hinted at by Mystagogue);
  2. having some waste-clearing system (analogous to our sewerage systems), perhaps a stand of specially cultivated plants that are known to be good clearers;
  3. And once the technology develops, perhaps a technological implementation of a device that can receive the required amount of water+waste, filter out the waste, and return the clean water back to the living environment. This could perhaps take the form of a cubicle or other enclosure where the elimination action could be done (in privacy), or perhaps some sort of suction head brought close to or in contact with the relevant body orifice (less private, perhaps more efficient).
  4. Privacy requirements would depend very much on the particular culture and its taboos.
  5. Cleaning would be less of an issue that for humans. No toilet paper equivalent probably needed.

Oh, and "bathroom" would probably be an incongruous term to them. Can't imagine someone bathing that is submerged in water for pretty much all of his life.


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