Tunisia has utilized a large portion of its moderate water potential. Needs increase exponentially as a result of population growth and socio-economic development. Since the 80's, Tunisia has resorted to desalination of brackish water and particularly via membrane techniques to supply the traditionally deficient regions with good quality water and come up with a solution for industrial water utilities. The choice and the management of desalination technologies must be studied. With this aim, a national research program has been established to dealing with the optimal management of existing units with a view to propose technological schemes more adapted to the quality of the raw water. In the present work, three plants are studied. The first one is an RO fed by water drawn from a subsoil aquifer. The operating parameters show that partial iron oxidation and chlorine are responsible for the short life of modules. The second deals with the water from a deep geothermal layer. Membrane autopsies show that the fouling is essentially biological and that the shock treatment has led to a significant improvement. The third one is an EDR plant fed by dam water. The main difficulty is the turbidity fluctuation, the instantaneous adjustment of the dose injected into flocculant and coagulant which has led to a substantial improvement of the plant performances. The follow up and diagnosis are presented and discussed in the light of new trends in material.