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” 😖
Lots of people drink bottled water, soda, beer, or other drinks not immediately connected to the water supply. Furthermore, poisons are unlikely to remain undetected long enough to kill the entire population. While a strong dose of a deadly poison like cyanide can kill in minutes it’s likely to be detected quickly due to how rapidly its effects begin to show up.
A slower-acting, accumulating poison like dimethylmercury could potentially kill more people because its effects don’t show up immediately. On the other hand, the delayed effects of the poison would provide the victims a chance to retaliate against the poisoners.
Either way, it’s a very crude and unfocused attack against a population which is unlikely to achieve any political aim besides wanton destruction and outrage.