Memories of my childhood come by reminding me of how I used to swim in the Danube river, until the age of 6 when after a walk along the coast I saw bodies of various animals rotting by the river, cows, pigs and many dead fish floating, I do not know to this day what caused their death but I've never swam again from that day.

This memory made me wonder about how medieval people drank their water, considering that rivers and lakes are and will always be nasty water sources. It is theorized that humans are so used and evolved to drink polluted water that our needs for B12 arisen from thousands of generations of drinking water contaminated with fecal bacteria, and in fact river and lake water is incredibly rich in B12 vitamin, a vitamin which naturally only forms in the gut of some animals and expelled with defecation.

and certainly a lil bit of feces in your water are not so deadly, I'm pretty sure some of that Danube water went in to my nose and some was absorbed by my skin, but I'm alive still, probably because I'm the result of the few humans who could tolerate a little fecal intoxication from swimming in polluted water. Billions of people swim every summer, and a lot of stuff is being dumped into beaches, not just feces but also t substances or plastic which transform into toxic stuff, Also the famous Hepatitis B happened because of a flood in England which discharged a lot of fecal matter into the sea, which was the absorbed by the world.

But imagine a creature which is way more sensitive than humans, a creature which needs a lot of purified water, what would be the least expensive and most natural way to clean their water? is it absurd to imagine a river covered in reeds and other pollution absorbing plants or algae? maybe reeds bred for the sole purpose to absorb as much toxic stuff as possible?

Probably taking down forests to burn some wood to boil water is not a good idea, and often burning bacteria only kills them but doesn't get rid of the toxic agents, people still get sick from contaminated meat even after roasting or boiling it completely and many parasites and viruses can withstand temperatures that would turn a steak into drywall.

  • $\begingroup$ You seem to be asking four completely separate questions: Bio-degradable wastewater (like fecal matter), and about long-lived wastewater contaminants like plastics and some chemicals. You are asking about the impacts of both on medieval folks and on a hypothetical clean-water organism. This seems like an I-am-wondering question (off-topic) instead of a question with a clear world-building purpose (on-topic). Please try to ask a single answerable question instead of four vague questions -- you will get much more satisfactory answers. $\endgroup$
    – user535733
    Jun 20, 2021 at 14:43
  • $\begingroup$ Fecal matter in the water isn't deadly? Tell that to someone who has contracted cholera as a result. Cholera is pretty much universally deadly unless treated. $\endgroup$
    – Monty Wild
    Jun 20, 2021 at 14:52
  • $\begingroup$ If you are just trying to avoid human provided contaminants, just locate your creature at the point where an underground river surfaces. Thousands of feet of bedrock is usually enough to keep our worst waste products out. Beyond that, check out the root adaptation of Mangrove trees. Perhaps once we are done here, similar adaptations will evolve to filter out all the stuff we leave behind. $\endgroup$ Jun 20, 2021 at 14:52
  • $\begingroup$ I'm not seeing a question in there, just a reminiscence and rambling comments about water. What is the actual question that is being asked? If it stems from that snippet which mentions "what would be the least expensive and most natural way to clean their water", then living rivers are some of the world's best filters. Augment with a sand & charcoal filter if your standards are higher. $\endgroup$
    – PcMan
    Jun 21, 2021 at 7:37

3 Answers 3


The story of humanity's relationship with water is a long one. For much of our history, we had no germ theory. Some societies simply drank whatever water was available, and some of the people who did so got sick, and some died as a result. However, if people are exposed to germs and survive, they tend to become immune, so the adults would have been resistant to the germs that might kill some of their kids. Diseases like dysentery, typhoid or cholera are spread by water, and have have killed a great many people.

A number of cultures independently developed a theory of clean water, that water that looked and smelled dirty was bad, and water that was clear was good, though they didn't know why. The ancient Romans had a working theory of water hygiene, but their lack of germ theory led to this being less than completely effective... but their system by which water was classified according to its quality would have helped significantly.

Without germ theory, it would be difficult to develop practises that would effectively prevent the transmission of waterborne diseases.

Water purification is a complex topic, but even in relatively primitive environments, there are steps that may be taken to purify water, including filtration, sedimentation and distillation.

It isn't possible to say in a SE answer exactly what steps must be taken to purify water in every situation... that could fill a book. One water source may be high in a few of the many different chemical contaminants, while another may be contaminated by a few of the many disease-causing organisms. The approach to treating contaminated water must address the specific contaminants.

However, as an example, Giardia is a common waterborne parasite that may be filtered effectively by passing water through simple, cheap, cloth filters.

  • 1
    $\begingroup$ Great submit. The story of water's relationship with humanity will be relatively short, I'm afraid.. $\endgroup$
    – Goodies
    Jun 20, 2021 at 16:10

The idea that drinking from streams would make you die was a myth. Most people lived in remote areas (farmsteads or small villages) with access to rain fed streams and natural springs- the access to clean water is why they would choose to live there. It wasn't as safe as modern water, but you could certainly drink it, and people routinely did. They didn't need to shit in the river, they could just walk outside to do it.

It's cities where it gets dicey, as the population density means that the more waste gets dumped. There they tended to boil water.

There was something else they could do. They could reroute the river. Leave a small branch for people to wash their stuff and dump their waste in, and take the larger branch for clean water. Digging a new route is pretty easy for a dedicated workforce and was often done with medieval tech.

Plants aren't gonna filter out all the shit that well. If you could magically make super plants you could do it, but the easiest way is to just divert the river and keep it clean.

  • $\begingroup$ I've never even heard of said myth that drinking from streams will make you die until your answer. Then again, I also implicitly know that this does not refer to a river that runs through a city. $\endgroup$
    – DKNguyen
    Jun 20, 2021 at 23:45
  • $\begingroup$ It's a popular idea that people only drank beer or something, and didn't drink water from streams. $\endgroup$
    – Nepene Nep
    Jun 21, 2021 at 10:55
  • $\begingroup$ I always thought that was only implicit to city river water. $\endgroup$
    – DKNguyen
    Jun 21, 2021 at 22:14


Wells work because their bottom is dug below the top of an aquifer, a water-permeable layer of rock. If you dig into it a little, the water will seep through the rock and collect into the well, which also cleans it

This is very easy to understand if you've ever dug holes in the sand at a beach, or right next to the edge of a river, usually if you dig just a few inches down you will hit the aquifer and your hole will begin to fill with water, to a point, despite no waves bringing in water to fill it. A well works exactly the same way, but much larger and more useful

You don't make any mention of the intelligence of your creatures, but you put forth boiling water to make it safe, implying fireproof containers, probably metal, which would imply a pretty high level of intelligence. More than enough intelligence to build wells

  • $\begingroup$ The trouble with wells is that they can be contaminated with chemicals rather than microorganisms. $\endgroup$
    – Monty Wild
    Jun 21, 2021 at 2:04
  • $\begingroup$ That's true, but the planets surface does work as a very effective filter. Also, OP didn't say much about the world, but I'm willing to bet that isn't an issue $\endgroup$ Jun 21, 2021 at 2:22

You must log in to answer this question.