It depends on .any thing most important is money. For most do gulf countries they have desalination treatment plant using RO.. also in Netherlands they do.

Regards

Try to google and make comparisons between world countries and you will find many countries that already using it. 

Also solar energy is widely used now In many countries.

Regards

What do you mean by different sources of salt water?

Could you define it?

The places that have adopted RO and other desalination techniques are those where the demand for water is higher than what is available as fresh water and there is the ability and willingness to pay. In many parts of the world there is a lack of safe drinking water but not really a lack of fresh water as a lot gets used for agriculture etc.  A lot of the world is a long way from the sea. RO is very expensive to operate and has a massive carbon footprint. Equally importantly it produces a lot of highly saline waste which has to go somewhere. Not so bad if you are sat on the coast of the Gulf but a bit more difficult in the middle of Australia. Solar panels are a way of providing the power but they are generally and so it might be more effective to use them for pumping groundwater in places where there is safe and less saline water in aquifers.

@mohamed 

What I meant by different sources of water is that the facility can obtain water from different seas/oceans and not just from a single source. 

Thank you for your response. 

@steve

Thank you for your response. I did not think of the possible scenario for the middle of Australia.