How long did it take for a well to be usable again after removing the carcass from it? Did it make the well unusable for years?
Two issues here. Toxic chemicals, and disease (bacteria and viruses).
- If something introduced toxic chemicals into the well, and the source for those chemicals has been removed, this is a question of how long it takes for the remaining chemicals already in there to become so diluted as to be no longer harmful. That depends on the type of chemical, how much got into the well, and the nature of the well itself (walls, water circulation, ...). Too many variables to come up with a number, or really, a range. I hope you agree.
Similar "too many variables" considerations apply to bacteria and viruses. However,
- Bacteria and viruses can be killed off by boiling the water prior to consumption. The issue is that, before the 19th century, people did not know about bacteria and viruses...
So... the answer really comes down to, it depends. The real danger with well poisoning was if it was not detected.