Anyway, water supply is non-issue. Next!Australians will not drink recycled water under any circumstances - research what happened at Toowoomba in 2006. And desalinated water is extremely expensive to produce, isn't environmentally friendly and runs directly against the stated aim to reduce carbon.
Water is indeed a problem in Australia - you should have been living in Melbourne ten years ago, it was bordering catastrophic.
The Qld govt spent $10B to install a 100% recycling plant which discharges in the dam, not into the pipes. So mother nature has her chance with it as well. Its not desirable but as Brisbane found out when it doesn't rain, drinking treated water is better than drinking urine or nothing, however it was not implemented this time due to rains coming. In the mean time its used by industry thus prolonging the dam capacity or off-setting population growth.
Also note there are some parts of Aus that already have recycled water in their water supply, Adelaide being one of them, unless you are going to tell me no one pee's in the Murry/Darling catchment. What happens to the waste water from all the towns upstream?
Desal water is NOT extremely expensive, the typical water cost in some Australian cities I looked up this morning is A$2-3/kL, my water costs are A$3.5/kL. Yes its more expensive but not alot more. However most of Australia's major catchment dams for the major cities are 40-80 years old, debts long paid off, built in close proximity to the cities, in ideal dam building locations because they could.
If you want to extend the water storage with new catchments, the locations are limited, expensive and comparable to desal and potentially more expensive, generally environmentally and community not acceptable and distant from the cities thus resulting in long distance pumping costs which is in itself expensive. Once you pump +100km, a Desal in an industrial area near saltwater water source starts looking very much more favorable.
In the case of Brisbane, the Mary River dam over 100km north of Brisbane was rejected by ALP Feds. Smaller more costly per kL dams were built in SW, one is not usable for water supply. Previous options such as the Wolfdem Dam and the other branch into the Brisbane river near Wivenhoe were all stopped by past ALP govts and now even if approved land prices are significantly higher. Desal and recycling is now the sole source for the future of water supply to Brisbane.
For Sydney, The only reasonable damable water course left was the Shoalhaven, coverted to a National Park by the NSW ALP govt to specifically prevent it from ever being dammed. The limited locations left are in the order of 150-200km away. Warragamba Dam is being looked at for yet another wall raising, which is pushing the catchmenmt less and less frequent heavy rains but beyond this Desal and recycling will be Sydney's future water supply options. A friend in NW leafy suburbs has an onsite treatment for his grey water for keeping is yard green. 20 years ago this would have been banned.
Adelaide and Perth's and future is in recycle and desal and I suspect Melbourne is not much better off.
Look up the boom in the desalination industry to see where the world is headed. If incorporated into processes with large volumes of waste heat such as power generation the costs can be much lower than stand alone desal and option even cheaper than catchment and this is what the middle east mostly does.
Having major cities running out of water and operating on tight water restrictions is not good for attracting business.