The Court of Owls secretly Illuminati’ing the place up.
Dr. Gotham, an evil warlock who was sealed under Gotham for millennia, radiating evil.
I wouldn’t be surprised if there was more then one company dumping shit into the water supply just to dodge having to pay to dispose of it properly, but compared to magical evil of varying degrees, it’s kind of a non-starter on the “This is why folks are nutso” chart.
Lol I like the thought that even though we see Batman stop Joker hundreds of times, one time Joker really did succeed and as a prank just put a smidge of toxin into the supply.
There is, variously:
I’m beginning to think that Gotham isn’t a good place to live.
that sounds like a few too many hellmouths in one place
Regarding item 7, Batman Returns had Christopher Walken’s character illegally dumping toxic waste, so yeah, there’s at least one known case.
Not to mention the half-dozen times the Joker tried to poison Gotham by putting Joker Toxin in the water supply
Lol I like the thought that even though we see Batman stop Joker hundreds of times, one time Joker really did succeed and as a prank just put a smidge of toxin into the supply.