They were cleaning the water towers at my building. :^K
They found a dead bird in one of the towers, they said the strong wind blew the lid open and that's probably how it got in.
Luckily it seems it was found just in time since the corpse hasn't started decaying or anything.

This is why I filter and boil my drinking water...

But I guess that means I, along with my entire building, have been bathing in dead bird water for at least 2 days or something.