Have you really considered how much water it takes to "make a verdant countryside"?
One (1) millimeter of rain spread over 1 square kilometer is 1 million liters, so the equivalent of a decent fall - say 100mm - is 100 megaliters per square km.
The current potential output of the Victorian desal plant is ~150 Gigaliters per year which would cover 1500 sq km with 100mm - an area about 39km x 39km - bugger all really.
The desal plant cost about $4billion and $600million per year to operate. then you have pipes, pumping stations etc.
Not to mention issues with hypersaline water that comes from desal plants that has potential to affect areas around the ocean outlets. Perhaps as town/water supplies it may be feasible.
