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” 😖
No.
But…
The adage that “the dose makes the poison” is working in your favor here. A large city supply delivers millions of liters of water per day; by the time you dilute your poison into millions of liters of water you’ll either be adding absurd amounts of poison (someone is going to notice massive line of tanker trucks queued up outside the treatment plant), or you are dealing with large - but not unweildly - volumes of something so horrendously toxic that it’s still deadly when diluted that much. There are very few substances that toxic, and someone is going to notice if you start procuring hundreds of liters of botulism toxin or Vx because at that point you are dealing with outlawed chemical warfare agents
Not only that, the water supply is linear, so to keep the water dangerous, you gotta keep adding the substance.
Just worth pointing out, changing water source in Flint Michigan and not adding corrosion inhibitors seemed to do an excellent job for a short period.
Oh yeah, that is the other way of poisoning a water supply, sabotage it so that it keeps poisoning itself
See also the Camelford disaster