Actually, water is only scarce in certain areas; there are some parts of Australia with an abundance of fresh water.
Many years ago, the bloke who designed the Harbour Bridge gave his name to a scheme to place high level dams in those areas (highlands of North Qld) and (mostly) use existing river systems to guide the water into the Darling system.
It was called the Bradfield scheme, I believe.
Obviously,these high level dams could also be used for Hydro.
A more imaginative approach could be to pump salt water, using wave/solar power up to high level reservoirs on the great divide. The salt water could then be fed through osmotic filters and hydro turbines, then released onto the western slopes.