I've rung there a few times. The first time I was still learning to control the bell, very much a beginner. As we came down the tower the captain drew my attention to the details of the bells. The number 5 (which I had been ringing) was cast in 1348 and has never been retuned. Depending upon the route he took and the time of day, Geoffrey Chaucer might have heard that bell which by then was already 50 years old. In 1348 Edward III created the Order of the Garter, and the black death reached our shores. People fight over Stradivarius violins citing their great age - the bell was 350 years old by then! Yet they trusted a beginner to ring it.
The view from the top of the tower is magnificent. Right across the river to Essex and both ways along the bank. Gently rolling fields going down to the river.
As regards water, I thought it was salt up to about the QEII bridge and brackish then up to London, but I'll willingly be corrected and accept that the boundaries are not fixed.