The poisoning of wells has been used as a wartime tactic since, well, since war was a thing. According to Metapedia, well poisoning was used as both an offensive tactic, to disrupt and depopulate a target area; and as a defensive tactic, to deny an invading army sources of clean water. “Rotting corpses (both animal and human) thrown down wells were the most common implementation; in one of the earliest examples of biological warfare, corpses known to have died from diseases such as bubonic plague or tuberculosis were especially favored.”
It’s such an effective tactic because It’s not obvious that a well has been poisoned. You can suspect, but it’s not like the water changes color, or that a skull and crossbones suddenly appears, warning everyone away. No big “HEY DON’T DRINK THIS” signs. But soon, those who have been to the well, particularly those who have drunk deeply, show manifestations.
A coolness, perhaps, or worse. Disparaging remarks to others that still reach your ears. And perhaps the most painful, avoidance. Of eye contact, of bumping into you, of ANY contact. Then you know for sure.
Innocent townspeople must have felt the same: What did we do to deserve this? We’re just over here, living our townspeople life, growing crops and stuff, trying to help our neighbors when they need it. Why you gotta go throw $h&! in my well?
The answer then, as now, is simple. It’s not about you, innocent townspeople. You’re just collateral damage in someone else’s battle.