It can be because of lead pipes in older buildings - but that is usually OK as long as you let the water run a bit before drinking - what you don’t want is to drink water that may have been standing in the pipes a long time. If it’s only passed through quite quickly, it should be OK.
I do think the bigger issue is there’s no absolute guarantee the tank is secured from the elements - things could have got in there and died, and you wouldn’t be any the wiser, so not recommended as drinking water. But I’ve done it loads of times, and so far, not come to any harm.
Though if they subsequently find MS is primarily contracted from contaminated drinking water, I guess I’ll know what happened.
I guessed the screaming thing might be a rat - or a rat attacking a starling, maybe? I know I have starlings in the loft space, and I think a rat might take a starling.
It was absolutely horrible, and I couldn’t do anything. I had to tell myself: “Well, nature is red in tooth and claw, and I just have to let it take its course.” But I dread to think what carnage could be up there to greet anyone brave enough to look. Haven’t noticed any offensive smells, so either it’s too enclosed to permeate the house, or there was an efficient predator, and there weren’t many remains left.