Regle
I doubt very much whether the water tower would have been chosen as an aiming point because, although it would stand out when viewed from ground level it would just be a very small circle viewed from above.
Thanks for your prompt reply. After submitting my post above I realised that the Water Tower viewed at night from 20,000 ft would have been a relatively insgnificant object, so I reckon my German neighbour got it wrong, although I suppose the tower
could have been an easily recognised landmark for ground attack aircraft sweeping in to attack Ruhr targets later in the war.