"...Poisoning the water supply for a major city..."
Years ago I read somewhere, don't recall where, that poisoning a large water supply was not all that feasible. Something to do with the large volume of water and the amount of "poison" that would be required. Maybe Doc Blast will know something about that...
That was me, here. I did the math for I forgot which poision, and what it would take to get ONE resevoir of the NYC system (The Ashokan in my example) up to the LD10 level (the amount of that poision needed to kill 10% of the people). I believe the poision I chose was Ricin, as it was the big scare going on at the time - the answer came out to be slightly more than 17 loaded tractor trailers worth
That was the day I stopped worrying so much
I know that sometime in the 1960s, someone dropped a 5 gallon bucked of LDS in there.... Made the news, that's about it