I have two tanks in the roof, one for heating and one tops up my cylinder. Old fashioned but very reliable and both plastic tanks are now around 45 years old. I did fit service taps to both as when originally installed, only one tap was fitted to cut off both tanks.
I am hoping Dave and Maz are not drinking tap water supplied from a roof tank although that was quite common many years ago.
In Exmouth about 25 years ago, i went to a house that had small bones coming from the tap. I removed 6 skeletons of birds that had walked up the large galvanised overflow pipe in the 1920 built house.
In my earlier message, i should have said all the other mains supplied outlets would work.