A desal plant in Australia is a good idea because it is an arid continent and is prone to drought. The biggest desal plant in the world was not a good idea. It was not required at the time and probably wont be required for another 20 years, especially given how well water restrictions worked during the drought.
Over-building on infrastructure is almost as bad as not building it at all. And as someone else pointed out this particular project was beset by dodgy builders, unions drinking at the trough and grandstanding politicians who wanted to be seen doing "something". All up, massive waste of money.
Fair enough. I must say from looking into it more that there seems to be an absurdly wide range of cost estimates being quoted, as well as a lot of mixing up of prices and costs, so the figures I quoted are probably bullshit.
Edit - I am not sure I agree with you about overbuilding on infrastructure though. A good example of this is the London sewer system by Joseph Bazalgette, that was massively overbuilt to the tune of twice the maximum requirement from what was considered the highest possible population density, just in case. Which was very lucky, given the development of the towerblock 100 years later.
Over-building on infrastructure is almost as bad as not building it at all. And as someone else pointed out this particular project was beset by dodgy builders, unions drinking at the trough and grandstanding politicians who wanted to be seen doing "something". All up, massive waste of money.