Dear Assia
Saline water is not commonly found in desert areas. Typically such water is highly brackish and is treated by brackish water reverse osmosis systems. The concetrate is ususally disposed to deeper aquifers not hydraulically connected to the brackish water aquifer. Not every desertous location has brackish water aqufers. Often these aquifers are very limited in size and recover very slowly - therefore they are not commonly used as water supply sources.
Nikolay Voutchkov