In the eighties I got called out to a posh'ish Hotel in London, the problem was the was no cold water coming through the taps of the third floor
Checked all valves ect thinking maybe some one been fiddling, all ok
checked tank, big galvanized thing, with a few boards spread over the top ,looked in, as my eyes adjusted, saw pigeon feathers floating on top, looked some more saw actually a few dead pigeons in side, looked down at the bottom and their was pigeon bones
There, were they had died, fallen in the tank, and rotted away
Anyway cut a long story short the blockage turned out to be pigeon skulls stuck in the cold feed pipework between the tank and the gate valve about six inches away
Cleaned it all out ect
So in answer to your question do I drink from tank water NO 🙂
especialy in old buildings,even brush my teeth with bottled water