My building’s water comes from a direct connection to the bore well (ground water) and overhead water tankers are all over 500 litres through which all taps in the house get water. I have crossed checked, there are 4 overhead tanks and each of them has a capacity of 1000 litres (i.e. 4000 litres in total).

Is my tap water considered Kurr? Please explain to clear my doubt.

It is Kur however it is not Jaree (running water). Hence ayatollah Sistani says that a person must wash 2 times and not just once as one does in the running water