WWT REUSE and mixing with rainwater

the need for water becomes more and more intense. So for real recovery, even see a total recovery of treated wastewater, such as Tunisia, which has around 300 million m3 / year and which suffers from a water shortage and whose call for unconventional resources, such as treated wastewater, are there methods or sectors that can reuse all of this resource? can mixing treated wastewater with rainwater be a good solution for significant reuse? are there any experiences in the world?