JohnWalker's first pic is indeed the Cathedral Water Tower, commonly known as 'The Baptistry', but should be called The Lavatory Tower. Dating from the early - mid twelfth century, only its lower half in unaltered, having originally had a rood above with up to eight water spouts for eight monks to wash at any one time. Dating from before 1165, it is shown on a contemporary map of the cathedral and precincts known as Prior Wibert's Waterworks Plan and was fed by natural springs beyond the walls of Canterbury, all of which is shown on the coloured map. This hydraulic system allowed water to run through pipework (mostly lead) to the tower after which it would be used to clean the necessarium, or reredorter (toilets) of the monastery. It would then flow into the Great Drain upon which it exited the city walls and into the City ditch.