Talla (and the Megget/Fruid) flow into Glencorse (the inflow is just above the dam), from where it is fed into Edinburgh.
The observant might have noticed a big new water treatment works being built opposite the Flotterstone Inn – and a big new pipe from there to Mortonhall.
Anyone who has been on the Castle Esplanade might also have been told the myth of cannonball house – that a cannonball fired from the castle became embedded in the wall. Actually, the building with the ball in it is a water cistern and the ball is at the same elevation as Glencorse Reservoir – i.e. the highest point in Edinburgh to which water will flow by gravity.