You don't have to tell me about the value of H2O
As I understand it,* Australian weather depends on El Nino and similar long-term changes in the Pacific, hence the extended periods of drought followed by wetter cycles. This suggests that the rains will return, although ten years is a weary long time to wait. (Wyoming has been waiting seven years so far, and it's supposed to have seasons.)
The answer, and it won't be cheap, is to diversify: wind- and nuclear-powered desalination, aggressive rainwater collection and storage (including underground storage -- a horrifically expensive undertaking for which your great-grand children will be very grateful), sewerage recycling (at least for irrigation), and research into more exotic schemes, such as that idea somebody had of sailing Antarctic bergs north and melting them in artificial basins close inshore. ("Exotic" sounds nicer than "harebrained," don't you agree? But who knows, it might be feasible, when water starts costing as much as petrol.) IOW, no one solution should be pursued: you need redundancy.
For god's sake, don't drill more boreholes. If you wreck your water-table, you might as well change your name to Ozymandias.
* If I understand it, which is a non-certainty.