There was also the Maroondah Aqueduct, which I read was built in 1886–1881 to supply water to the Preston Reservoir. This, too, has been closed in a number of places and there's a walking/biking trail along part of it. There's also a disused section of this aqueduct that intersects the Yarra Glen to Christmas Hills Road.
Although in this era of steel pipes, we tend to think of this technology as a bit "yesterday", in fact there are still sections of the Maroondah Aqueduct in use today. There's a reference here to over 30 kms of it still being in use (but my limited googling hasn't confirmed this distance).
Here's a link showing the location of the section of the aqueduct where it passes behind Balgownie Estate (the big while blobs are the accommodation blocks).