Desalination is costly, but when droughts are occurring it can be less expensive than other sources of water. unfortunately they cannot be turned on and off easily. Sydney has government owned systems that they will start powering up and cycling 3-6 months before they can produce significant volumes for use so they start turning them up well before droughts reach that point.

That is the same issue with some of California. There is a project going by the name of Poseidon in Southern California where private investors are trying to get contracted to build desalination facilities, but part of that agreement requires the local communities to purchase minimum amounts of water if they need it or not. The private companies do not want to cycle the plant down and loose their income, so they want to shift that cost onto the taxpayers and local utility company.