Random thoughts just popped in my head and I just remembered that all the water in a given city is all centralized. Just add poison and boom, eradicated an entire city who are full of dissidents/opposition as punishment for voting the “wrong” way, or for a protest, or if the population is filled with “filthy undesirable [Insert Racial Group Here]”, or something like that.
Kinda unsettling to see that we are all just attached to “the grid” 😖
The chance of them pulling it off with nobody noticing or saying anything is very low, it’s not a one person operation. Then depending on the speed of the poison it would become obvious that there’s something in the water very quickly and people would stop drinking it.